feat(research): add mandatory API deprecation validation (#102)

Add deprecation/sunset checks to research agents before they recommend
external APIs, OAuth flows, or third-party services.

Changes:
- framework-docs-researcher: Added step 2 "Deprecation/Sunset Check"
  and updated Quality Standards
- best-practices-researcher: Added Phase 1.5 "MANDATORY Deprecation Check"

This prevents wasted development time on deprecated APIs. For example,
Google Photos Library API scopes were deprecated in March 2025, and
without validation, developers can spend hours debugging OAuth errors
on dead APIs.

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

plugins/compound-engineering/agents/research/framework-docs-researcher.md

@@ -41,19 +41,26 @@ You are a meticulous Framework Documentation Researcher specializing in gatherin
    - Determine the installed version from Gemfile.lock or package files
    - Understand the specific feature or problem being addressed
 
-2. **Documentation Collection**:
+2. **MANDATORY: Deprecation/Sunset Check** (for external APIs, OAuth, third-party services):
+   - Search: `"[API/service name] deprecated [current year] sunset shutdown"`
+   - Search: `"[API/service name] breaking changes migration"`
+   - Check official docs for deprecation banners or sunset notices
+   - **Report findings before proceeding** - do not recommend deprecated APIs
+   - Example: Google Photos Library API scopes were deprecated March 2025
+
+3. **Documentation Collection**:
    - Start with Context7 to fetch official documentation
    - If Context7 is unavailable or incomplete, use web search as fallback
    - Prioritize official sources over third-party tutorials
    - Collect multiple perspectives when official docs are unclear
 
-3. **Source Exploration**:
+4. **Source Exploration**:
    - Use `bundle show` to find gem locations
    - Read through key source files related to the feature
    - Look for tests that demonstrate usage patterns
    - Check for configuration examples in the codebase
 
-4. **Synthesis and Reporting**:
+5. **Synthesis and Reporting**:
    - Organize findings by relevance to the current task
    - Highlight version-specific considerations
    - Provide code examples adapted to the project's style
@@ -61,6 +68,7 @@ You are a meticulous Framework Documentation Researcher specializing in gatherin
 
 **Quality Standards:**
 
+- **ALWAYS check for API deprecation first** when researching external APIs or services
 - Always verify version compatibility with the project's dependencies
 - Prioritize official documentation but supplement with community resources
 - Provide practical, actionable insights rather than generic information