Add P1-T10 and P4-T2: document and fix Xcode first-approval timing race in broker mode

[SoundBlaster]

Description

Adds two new open tasks to SPECS/Workplan.md identified during live multi-client broker+Web UI testing (Zed + Claude Code):

P1-T10 — Document Xcode first-approval timing race in Troubleshooting & Known Issues
When broker mode is used for the first time, Xcode shows a per-process approval dialog. MCP clients that connect before approval is granted receive an empty tools/list and cache it permanently, showing 0 tools with a green connected indicator and no actionable error. Documents root cause, correct first-time setup sequence, and recovery steps.

P4-T2 — Cache tools/list in broker and gate client responses on upstream readiness
Fix the underlying race by: (1) blocking client requests until the upstream completes a successful initialize round-trip, retrying with backoff if upstream exits early; (2) caching the tools/list response after upstream init so all clients receive tools instantly without per-client upstream round-trips. Eliminates the Xcode approval timing race without requiring any user intervention.

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactoring
• CI/CD improvement

Quality Gates

• make test - All tests pass with ≥90% coverage
• make lint - No linting errors
• make format - Code is properly formatted
• make typecheck - Type checking passes
• make doccheck - Documentation is synced with DocC (if docs changed)

Workplan-only change — no source, tests, or docs modified. Quality gates N/A for this PR.

Documentation Sync

• Documentation changes are synced with DocC catalog (or N/A)

Testing

• Added/updated tests for new functionality
• All tests pass locally
• Manually tested the changes

Task entries verified for correct ID uniqueness, dependency references, and acceptance criteria testability.

Checklist

• Code follows the project's style guidelines
• Self-review completed
• Comments added for complex code
• Documentation updated (if needed)
• No new warnings generated
• PR title is descriptive