docs: fix broken MessageDelivery API reference links in state_variables.md (#23801)

## What

Fixes the 3 broken API reference links flagged by the docs
`validate:api-ref-links` checker (reported in #docs-alerts against PR
#23695):

```
docs-developers/docs/aztec-nr/framework-description/state_variables.md
  -> aztec-nr-api/mainnet/noir_aztec/messages/message_delivery/struct.MessageDelivery
```

## Why they were broken (validated)

The links targeted
`struct.MessageDelivery#method.{onchain_constrained,onchain_unconstrained,offchain}`.
In the docs build `#api_ref_version` resolves to **`mainnet`** (v4.3.0),
and the committed `static/aztec-nr-api/mainnet/` snapshot does **not**
contain `struct.MessageDelivery.html`. In v4.3.0 the symbol is exposed
as a global:

- `noir_aztec/messages/message_delivery/global.MessageDelivery.html` ✓
(exists)
- `noir_aztec/messages/message_delivery/struct.MessageDeliveryEnum.html`
✓ (exists)
- `noir_aztec/messages/message_delivery/struct.MessageDelivery.html` ✗
(does not exist)

The page source was updated to describe the newer method-based
`MessageDelivery` struct API (which matches current `next` code and the
`#include_code` example on the page), but `#api_ref_version` still pins
API-ref links to the released mainnet snapshot, so
`struct.MessageDelivery` 404s. The prose/examples are left unchanged
because they correctly match the current code.

These links are **pre-existing on `next`**; PR #23695 only touches
governance/token docs and did not introduce them — the checker simply
surfaced them on that PR.

## Fix

Repoint the three links to `global.MessageDelivery`, the page that
documents `MessageDelivery` in the pinned mainnet API. The per-method
anchors are dropped since the global page has none.

## Validation

`scripts/validate_api_ref_links.sh` over the preprocessed page (with
`#api_ref_version` resolved to `mainnet`):

- Before: `Broken links: 3`
- After: `Broken links: 0` (`Version mismatches: 0`)

---
*Created by
[claudebox](https://claudebox.work/v2/sessions/97d92d02ac088b2d) ·
group: `slackbot`*

Author: critesjosh

docs/docs-developers/docs/aztec-nr/framework-description/state_variables.md

@@ -273,9 +273,9 @@ When working with private state variables, many operations return a `NoteMessage
 #### Delivery Methods
 
 Private notes need to be communicated to their recipients so they know the note exists and can use it. The [`NoteMessage`](pathname:///aztec-nr-api/#api_ref_version/noir_aztec/note/struct.NoteMessage) wrapper forces you to make an explicit choice about how this happens:
-  - [`MessageDelivery::onchain_constrained()`](pathname:///aztec-nr-api/#api_ref_version/noir_aztec/messages/message_delivery/struct.MessageDelivery#method.onchain_constrained): Verified in the circuit (most secure, but highest cost) - Use when the sender cannot be trusted to deliver correctly (e.g., protocol fees, multisig config updates). **Warning:** Currently [not fully constrained](https://github.com/AztecProtocol/aztec-packages/issues/14565) - the log's tag is unconstrained.
-  - [`MessageDelivery::onchain_unconstrained()`](pathname:///aztec-nr-api/#api_ref_version/noir_aztec/messages/message_delivery/struct.MessageDelivery#method.onchain_unconstrained): Message stored onchain but no guarantees on content - Use when the sender is incentivized to deliver correctly but may not have an offchain channel to the recipient.
-  - [`MessageDelivery::offchain()`](pathname:///aztec-nr-api/#api_ref_version/noir_aztec/messages/message_delivery/struct.MessageDelivery#method.offchain): Lowest cost, no onchain data - Use when the sender and recipient can communicate and the sender is incentivized to deliver correctly.
+  - [`MessageDelivery::onchain_constrained()`](pathname:///aztec-nr-api/#api_ref_version/noir_aztec/messages/message_delivery/global.MessageDelivery): Verified in the circuit (most secure, but highest cost) - Use when the sender cannot be trusted to deliver correctly (e.g., protocol fees, multisig config updates). **Warning:** Currently [not fully constrained](https://github.com/AztecProtocol/aztec-packages/issues/14565) - the log's tag is unconstrained.
+  - [`MessageDelivery::onchain_unconstrained()`](pathname:///aztec-nr-api/#api_ref_version/noir_aztec/messages/message_delivery/global.MessageDelivery): Message stored onchain but no guarantees on content - Use when the sender is incentivized to deliver correctly but may not have an offchain channel to the recipient.
+  - [`MessageDelivery::offchain()`](pathname:///aztec-nr-api/#api_ref_version/noir_aztec/messages/message_delivery/global.MessageDelivery): Lowest cost, no onchain data - Use when the sender and recipient can communicate and the sender is incentivized to deliver correctly.
 
 #include_code note_delivery /noir-projects/noir-contracts/contracts/app/private_token_contract/src/main.nr rust