feat(BRIDGE-WP-0003): MCP server, /bridge-status skill, cross-mode coverage enforcement

Implements the full BRIDGE-WP-0003 workplan: 188 tests passing, 0 lint errors.

## What's added

**Capability registry** (`src/bridge/capabilities.py`):
- 10 capabilities with required_access_modes (cli/mcp/skill)
- Single source of truth for what OpsBridge does and where

**MCP server** (`src/bridge/mcp_server/server.py`):
- 10 FastMCP tools: bridge_up/down/restart/status/logs + 5 catalog_* tools
- 3 resources: bridge://status, catalog://domains, catalog://targets
- `.mcp.json` for project-scope auto-registration
- `scripts/register_mcp.py` for user-scope machine-global registration

**Skill** (`~/.claude/plugins/ops-bridge/bridge-status.md`):
- /bridge-status: health table with emoji indicators + remediation advice

**Cross-mode test coverage enforcement**:
- `tests/conftest.py`: capability/access_mode marks + collect_capability_coverage()
- `tests/test_mcp.py`: 31 FastMCP in-process client tests (Client(mcp) pattern)
- `tests/test_skill.py`: static skill lint against capability registry
- `tests/test_coverage_completeness.py`: meta-test that fails if any required
  (capability × mode) pair lacks a test; also validates CLI commands and MCP
  tools are registered in the capability registry

**ADR** (`architecture/adr-001-cross-mode-capability-registry.md`):
- Documents the registry pattern and FastMCP 3.x testing approach

Key implementation note: FastMCP 3.x in-process results are in
result.content[0].text (JSON string), not result.data directly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_integration.py

@@ -1,9 +1,5 @@
 """Integration tests for OpsBridge."""
-import json
-import os
 import textwrap
-import time
-from pathlib import Path
 from unittest.mock import MagicMock, patch
 
 import pytest
@@ -132,7 +128,7 @@ class TestReconnectLoop:
 class TestHealthCheckDegradedPath:
     def test_degraded_state_on_health_failure(self, state_dir):
         """Health check failure sets state to DEGRADED."""
-        from bridge.health import HealthChecker, HealthResult
+        from bridge.health import HealthResult
 
         hc_cfg = MagicMock()
         hc_cfg.url = "http://127.0.0.1:19001/health"
@@ -170,9 +166,7 @@ class TestHealthCheckDegradedPath:
             return proc
 
         failed_result = HealthResult(ok=False, error="connection refused")
-        recovered_result = HealthResult(ok=True, status_code=200)
 
-        import asyncio
 
         async def fake_check_failing():
             return failed_result