feat: add unified_review MCP prompt + sync tool/prompt counts

Adds the unified_review MCP prompt (invoked as /code-review-graph:unified_review)
that drives the unified-review workflow: graph context -> detect_changes ->
score_review -> findings -> dedupe_findings -> generate_report. READ-ONLY:
every finding waits for a manual fix decision. Takes base and tier
(fast/standard/strict) arguments.

- prompts.py: unified_review_prompt + docstring count 5->6
- main.py: @mcp.prompt() registration
- tests/test_prompts.py: TestUnifiedReviewPrompt + preamble test
- docs: LLM-OPTIMIZED-REFERENCE, COMMANDS, CLAUDE.md, INDEX, architecture,
  README + 4 localized READMEs; tool count 30->31 and prompt count 5->6
  synced (historical ROADMAP/FEATURES version notes left unchanged)

docs/architecture.md

@@ -20,7 +20,7 @@
 │  ┌────────────────────────────────────────────┐              │
 │  │      MCP Server (stdio or localhost HTTP)  │              │
 │  │                                            │              │
-│  │  30 MCP Tools + 5 MCP Prompts              │              │
+│  │  31 MCP Tools + 6 MCP Prompts              │              │
 │  │  ├── Core: build, impact, query, review,   │              │
 │  │  │   search, traverse, embed, stats, docs  │              │
 │  │  ├── Flows: list, get, affected            │              │