Document and test all four error pages' recovery flows in ERROR_PAGES_README.md

[1nonlypiece]

📌 Description

ERROR_PAGES_README.md exists but does not fully document the behaviour and
recovery actions of the live error surfaces (error.tsx, not-found.tsx,
network-error, transaction-error), including how transaction-error maps
error categories to recovery CTAs. Contributors lack a single reference for the
intended UX of each error state.

This issue brings ERROR_PAGES_README.md up to date with the implemented pages
and their recovery flows, with a small drift-guard test.

🎯 Requirements and Context

• Document each error page's purpose, triggers, copy, and recovery actions.
• Document the transaction-error category→CTA mapping and network-error
  retry/countdown behaviour.
• Cross-link from README.md.
• Add a test that the documented page paths exist (guard against drift).

🛠️ Suggested Execution

1. Fork the repo and create a branch

git checkout -b docs/error-pages-readme

2. Implement changes

• Update ERROR_PAGES_README.md to reflect the current pages and flows.
• Add src/app/__tests__/errorPagesDoc.test.ts asserting documented page paths
  exist and key recovery CTAs are present.
• Validate the doc matches the implemented behaviour.

3. Test and commit

• Run pnpm test.
• Cover edge cases: missing page flagged, CTA label drift, new error route added.

Example commit message

docs: update ERROR_PAGES_README with recovery flows and drift test

✅ Guidelines

• Minimum 95% test coverage on the drift-guard helper.
• Clear, reviewer-friendly documentation.
• Timeframe: 96 hours.

🏷️ Labels

type-documentation · area-frontend · MAYBE REWARDED · GRANTFOX OSS ·
OFFICIAL CAMPAIGN

💬 Community & Support

• Join the CommitLabs contributor Discord to coordinate and get unblocked fast:
  https://discord.gg/WV7tdYkJk
• Introduce yourself before starting so we can avoid duplicate work and pair you
  with a reviewer. Maintainers triage actively and review fast.

[GBOYEE]

I'd like to work on this.

Approach:

• I'll write the test cases and ensure they pass with full coverage
• Verify with existing tests + add new ones if needed

Estimated effort: ~1-2 hours. PR incoming shortly.

[GBOYEE]

I'd like to work on this.

Approach:

• I'll write the test cases and ensure they pass with full coverage
• Verify with existing tests + add new ones if needed

Estimated effort: ~1-2 hours. PR incoming shortly.

[GBOYEE]

I'd like to work on this.

Approach:

• Read the relevant codebase and understand the scope
• Implement the changes with clean, tested code
• Verify with existing tests + add new ones

Estimated effort: ~1-2 hours. PR incoming shortly. Closes #661

[GBOYEE]

I'd like to work on this issue.

My Approach

• Analyze the root cause of: ##
• Implement a clean, tested fix
• Follow existing code patterns and conventions

Files Likely Modified

• TBD after analysis

Timeline

• Estimated completion: 15-30 minutes
• PR will be submitted with tests and documentation

Closes #661