feat(docs): apply FPC docs to developer versioned docs (#22541)

## Summary

- Ports changes from #22496 (Nethermind FPC docs) and #22497 (private
FPC guide) to the `v4.2.0-aztecnr-rc.2` developer versioned docs
- Updates `how_to_pay_fees.md` with new payment methods table,
deprecation notice, third-party FPC section (Nethermind example), and
private fee payment section
- Updates `fees.md` (foundational topics) with expanded FPC payment
methods description, new "How FPCs work" section, and teardown phase
clarification
- Updates `how_to_create_account.md` anchor links to match renamed
heading
- Adds new `how_to_use_private_fee_juice.md` guide (DeFi Wonderland's
PrivateFPC)

## Test plan

- [ ] `yarn start` in `docs/` — verify versioned pages render correctly
- [ ] Confirm internal links resolve (anchors to
`#sponsored-fpc-devnet-and-local-only`,
`#third-party-fpcs-on-testnet-and-mainnet`, `#how-fpcs-work`, and the
new private FPC guide)
- [ ] Verify external links to Nethermind and Wonderland repos are valid

Author: critesjosh

docs/developer_versioned_docs/version-v4.2.0/docs/aztec-js/how_to_pay_fees.md

@@ -109,7 +109,7 @@ const { receipt: feeJuiceReceipt } = await token.methods
   .mint_to_public(aliceAddress, 1n)
   .send({
     from: aliceAddress,
-    // no fee payment method needed — Fee Juice is used automatically
+    // no fee payment method needed; Fee Juice is used automatically
   });
 console.log("Transaction fee:", feeJuiceReceipt.transactionFee);
 ```
@@ -172,34 +172,34 @@ const { receipt: tx } = await bananaCoin.methods
 > <sup><sub><a href="https://github.com/AztecProtocol/aztec-packages/blob/v4.2.0/yarn-project/end-to-end/src/e2e_fees/sponsored_payments.test.ts#L57-L68" target="_blank" rel="noopener noreferrer">Source code: yarn-project/end-to-end/src/e2e_fees/sponsored_payments.test.ts#L57-L68</a></sub></sup>
 
 
-### Private Fee Payment
+### Private fee payment
 
-For transactions where the fee payment itself should be private, you can use a fully private FPC — one that holds Fee Juice claimed from L1 as an internal private balance, works on every network, and never needs an onchain deployment. See [Pay Fees Privately](./how_to_use_private_fee_juice.md) for how this pattern works and a walkthrough using a community-built example.
+For transactions where the fee payment itself should be private, you can use a fully private FPC, one that holds Fee Juice claimed from L1 as an internal private balance, works on every network, and never needs an onchain deployment. See [Pay Fees Privately](./how_to_use_private_fee_juice.md) for how this pattern works and a walkthrough using a community-built example.
 
 :::tip Shared salt for privacy
-When multiple apps derive the same private FPC address (using the same artifact and salt), every private fee payment joins a single, larger privacy set. See [Recommended salt](./how_to_use_private_fee_juice.md#recommended-salt-0) for details.
+When multiple apps derive the same private FPC address (using the same artifact and salt), every private fee payment joins a single, larger privacy set. See [recommended salt](./how_to_use_private_fee_juice.md#recommended-salt-0) for details.
 :::
 
 ### Third-party FPCs on testnet and mainnet
 
-On networks where the Sponsored FPC is unavailable, third-party FPCs deployed by ecosystem teams let you pay fees in tokens other than Fee Juice. Each FPC provider typically offers an SDK or API that handles payment method construction on the client side — this may include quote fetching and authwit creation, though the exact flow depends on the FPC design. For background on how FPCs work at the protocol level, see [How FPCs work](../foundational-topics/fees.md#how-fpcs-work).
+On networks where the Sponsored FPC is unavailable, third-party FPCs deployed by ecosystem teams let you pay fees in tokens other than Fee Juice. Each FPC provider typically offers an SDK or API that handles payment method construction on the client side. This may include quote fetching and authwit creation, though the exact flow depends on the FPC design. For background on how FPCs work at the protocol level, see [how FPCs work](../foundational-topics/fees.md#how-fpcs-work).
 
 #### Example: Nethermind Private Multi Asset FPC
 
-To illustrate how a third-party FPC integration works, the following walkthrough uses Nethermind's [Private Multi Asset FPC](https://github.com/NethermindEth/aztec-fpc) as a reference. This is one implementation — other FPCs may differ in design and API.
+To illustrate how a third-party FPC integration works, the following walkthrough uses Nethermind's [Private Multi Asset FPC](https://github.com/NethermindEth/aztec-fpc) as a reference. This is one implementation, other FPCs may differ in design and API.
 
 This FPC is quote-based and operates privately:
 
-- A single deployment accepts many tokens — the asset is selected per quote rather than hard-coded at deploy time.
+- A single deployment accepts many tokens. The asset is selected per quote rather than hard-coded at deploy time.
 - Fee payments are transferred as private notes, so fee activity is not visible onchain.
 - An operator-run attestation service signs per-user quotes binding the FPC address, accepted asset, amounts, expiry, and user.
-- A cold-start entrypoint allows a brand-new account to bridge tokens from L1, claim on L2, and pay the fee in a single transaction. Note that the cold-start path calls `Token::mint_to_private`, which enqueues a public call to update the token's total supply — so the minted amount is visible onchain even though the user's identity and balances remain private.
+- A cold-start entrypoint allows a brand-new account to bridge tokens from L1, claim on L2, and pay the fee in a single transaction. Note that the cold-start path calls `Token::mint_to_private`, which enqueues a public call to update the token's total supply, so the minted amount is visible onchain even though the user's identity and balances remain private.
 
 :::warning Third-party software
-This FPC is developed and maintained by Nethermind, not by Aztec Labs. The SDK (`@nethermindeth/aztec-fpc-sdk`) may not yet be published to npm — check the [repository README](https://github.com/NethermindEth/aztec-fpc/blob/main/sdk/README.md) for current install instructions. Review the [protocol spec](https://github.com/NethermindEth/aztec-fpc/blob/main/docs/spec/protocol-spec.md) and evaluate independently before integrating.
+This FPC is developed and maintained by Nethermind, not by Aztec Labs. The SDK (`@nethermindeth/aztec-fpc-sdk`) may not yet be published to npm; check the [repository README](https://github.com/NethermindEth/aztec-fpc/blob/main/sdk/README.md) for current install instructions. Review the [protocol spec](https://github.com/NethermindEth/aztec-fpc/blob/main/docs/spec/protocol-spec.md) and evaluate independently before integrating.
 :::
 
-The SDK wraps the quote-and-pay flow into a single call. The snippet below shows the general shape of the integration (illustrative — verify against the current SDK API before using):
+The SDK wraps the quote-and-pay flow into a single call. The snippet below shows the general shape of the integration (illustrative; verify against the current SDK API before using):
 
 ```ts
 import { FpcClient } from "@nethermindeth/aztec-fpc-sdk";
@@ -282,7 +282,7 @@ import { FeeJuicePaymentMethodWithClaim } from "@aztec/aztec.js/fee";
 // Create a payment method that claims the bridged Fee Juice and uses it to pay
 const bridgePaymentMethod = new FeeJuicePaymentMethodWithClaim(feeJuiceAccount.address, claim);
 
-// Use it to pay for any transaction — here we deploy the account in one step
+// Use it to pay for any transaction; here we deploy the account in one step
 const deployMethodBridged = await feeJuiceAccount.getDeployMethod();
 await deployMethodBridged.send({
   from: NO_FROM,
@@ -338,7 +338,7 @@ Note that `gasLimits` and `teardownGasLimits` use `daGas`/`l2Gas` field names, w
 ### Use automatic gas estimation
 
 :::note
-When using `EmbeddedWallet`, gas estimation happens automatically on every `send()` — you don't need to pass `estimateGas`. This option is useful for custom wallet implementations or when you want to estimate gas during a `simulate()` call.
+When using `EmbeddedWallet`, gas estimation happens automatically on every `send()`; you don't need to pass `estimateGas`. This option is useful for custom wallet implementations or when you want to estimate gas during a `simulate()` call.
 :::
 
 ```typescript title="auto_gas_estimation" showLineNumbers