fix(api): validate Solana author route params

[dirtybits]

Summary

• reject malformed non-EVM author path parameters before Solana trust, dispute, or identity lookups
• use the shared chain-address boundary helper with the configured Solana context; preserve the existing Base/EVM path unchanged
• add a no-side-effect regression and update the successful GET fixture to a valid Solana address
• record the focused implementation and validation in .agents/plans/validate-author-route-pubkey.plan.md

Test plan

• npm test --workspace @agentvouch/web -- __tests__/api/author-route.test.ts --maxWorkers=1 --no-fileParallelism (7 tests)
• npm run format:check
• npm run lint:web
• npm run typecheck
• npm test --workspace @agentvouch/web -- --maxWorkers=1 --no-fileParallelism (128 files / 928 tests)
• npm exec --workspace @agentvouch/web -- next build --webpack
• git diff --check

Notes

No live Solana RPC, browser, wallet, database, or deployment flow was run. The webpack build passed with the repository's existing ox/viem dynamic-import warning and expected static-generation DATABASE_URL fallback logs because local database credentials are absent.