fix(sol): use pinned compiler for bb sol build (#24620)

## Summary
- Move the `barretenberg/sol` Foundry `solc` setting into
`[profile.default]`.
- This makes `bb-sol` use the compiler already downloaded by
`l1-contracts-solc` instead of invoking Foundry's SVM network installer
during `forge build`.

## Investigation
[PR #24606](#24606)
entered the merge queue at 2026-07-08 22:51:37 UTC and was removed at
23:03:01 UTC. The failing merge-group run was [CI3 run
28981250165](https://github.com/AztecProtocol/aztec-packages/actions/runs/28981250165)
on queue SHA `fddbdbb79591f5cda6fa6450157e180cbfddb89f`.

The failed status was `ci/a1-fast`; the underlying `bb-sol` log shows
`forge build` in `barretenberg/sol` tried to install `solc 0.8.30` from
`raw.githubusercontent.com/nikitastupin/solc/.../linux/aarch64/solc-v0.8.30`
and got HTTP 429. `l1-contracts-solc` had already succeeded from cache,
so the problem was that Foundry ignored the pinned compiler setting
because it was scoped under `[fuzz]`.

## Verification
- `forge config --json` in `barretenberg/sol` now reports `"solc":
"../../l1-contracts/solc-0.8.30"`.
- `./bootstrap.sh download_solc` in `l1-contracts` passed.
- `make bb-sol` passed.
- `./bootstrap.sh ci` was attempted but this branch's root bootstrap
does not define `ci` (`Unknown command: ci`; available modes are
`ci-fast`, `ci-full`, `ci-full-no-test-cache`).
- `./bootstrap.sh ci-fast` was attempted; the local workspace stopped
before `bb-sol` because `.claude/tests/agents_symlink_test` fails
against the harness-provided `AGENTS.md`/agents symlink layout. The
affected `bb-sol` target was verified directly above.

---
*Created by
[claudebox](https://claudebox.work/v2/sessions/2b8c305bd7244e7e) ·
group: `slackbot`*

Author: AztecBot

barretenberg/sol/foundry.toml

@@ -9,14 +9,14 @@ gas_limit = 900000000000000000
 bytecode_hash = "none"
 evm_version = "cancun"
 
-[fuzz]
-runs = 2
-
 # Use the pre-downloaded solc binary from l1-contracts. l1-contracts' build is
 # the single owner of the svm download; pointing other forge projects at the
 # same binary avoids parallel svm downloads racing on ~/.svm.
 solc = "../../l1-contracts/solc-0.8.30"
 
+[fuzz]
+runs = 2
+
 [lint]
 ignore = ["./lib/**"]
 exclude_lints = [