P13-T1: Design persistent broker architecture and protocol contract

[SoundBlaster]

Description

Delivers P13-T1: the architecture specification and initial module scaffold for the persistent broker subsystem (Phase 13). No production logic is implemented yet — this task produces the design documents, type definitions, and stub classes that P13-T2 through P13-T4 will fill in.

Key deliverables:

• SPECS/ARCHIVE/P13-T1_.../broker_architecture_spec.md — full lifecycle state machine, sequence diagrams, and ID-remapping correlation strategy
• ADR-001 through ADR-004 embedded in the PRD: UDS transport, peer-UID security, socket path, reconnect backoff
• src/mcpbridge_wrapper/broker/ — new package with types.py, daemon.py, transport.py, proxy.py, __init__.py (stubs only; all methods raise NotImplementedError until P13-T2/T3/T4)
• tests/unit/test_broker_stubs.py — 23 tests covering type contracts, config defaults, and NotImplementedError guarantees

Type of Change

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

Quality Gates

• make test - All tests pass with ≥90% coverage (495 passed, 5 skipped; 96.06%)
• make lint - No linting errors (ruff check src/ clean)
• make format - Code is properly formatted
• make typecheck - Type checking passes (mypy src/ — 18 files, no issues)
• make doccheck - Documentation is synced with DocC (N/A — no docs/ changes)

Documentation Sync

• Documentation changes are synced with DocC catalog (or N/A) — N/A, no docs/ files changed

Testing

• Added/updated tests for new functionality (23 new tests in test_broker_stubs.py)
• All tests pass locally
• Manually tested the changes — N/A for design/stub task; no executable behavior to test

Checklist

• Code follows the project's style guidelines
• Self-review completed
• Comments added for complex code (all stub methods document their future implementation task)
• Documentation updated (if needed) — PRD archived, Workplan.md updated, INDEX.md updated
• No new warnings generated
• PR title is descriptive