Add manual AI analysis trigger for existing feedback

Implement dashboard functionality to manually trigger AI analysis for
feedback that was submitted before Phase 4 or failed analysis. Adds
detection mechanism to identify which feedback has been analyzed.

Features:
- Manual analysis trigger route: POST /feedback/{id}/analyze
- Detection of whether feedback has been analyzed (analysis.md exists)
- Dashboard UI button showing "Analyze" or "Re-analyze"
- Visual feedback for feedback without text content
- Comprehensive error handling and flash messages

Implementation:
- app/routes/dashboard.py: Added trigger_analysis() route handler
- app/routes/dashboard.py: Updated detail() to pass analysis status
- app/services/feedback_storage.py: Added has_analysis() helper method
- app/templates/dashboard/detail.html: Added analyze button UI
- tests/contract/test_dashboard_routes.py: Added 3 new contract tests

Testing:
- test_post_trigger_analysis_success: Successful manual analysis
- test_post_trigger_analysis_no_content: Reject empty content
- test_post_trigger_analysis_unauthenticated: Auth required
- All 49 tests passing (1 skipped)

User Experience:
- Green box with "Analyze" button for unanalyzed feedback
- Blue box with "Re-analyze" button for already analyzed feedback
- Red box with info message for feedback without text content
- Flash messages show success/error after analysis

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/templates/dashboard/detail.html

@@ -67,6 +67,30 @@
         </form>
     </div>
 
+    <!-- AI Analysis Trigger -->
+    {% if can_analyze %}
+    <div style="margin: 20px 0; padding: 15px; {% if has_analysis %}background: #d1ecf1;{% else %}background: #d4edda;{% endif %} border-radius: 5px;">
+        <form method="post" action="{{ url_for('dashboard.trigger_analysis', feedback_id=feedback.feedback_id) }}" style="display: flex; align-items: center; gap: 10px;">
+            <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
+            {% if has_analysis %}
+                <span style="font-size: 1.2em;">🔄</span>
+                <label><strong>Re-run AI Analysis:</strong> This feedback has been analyzed. Click to re-analyze.</label>
+            {% else %}
+                <span style="font-size: 1.2em;">🤖</span>
+                <label><strong>Run AI Analysis:</strong> This feedback has not been analyzed yet.</label>
+            {% endif %}
+            <button type="submit" style="padding: 5px 15px; background: #007bff; color: white; border: none; border-radius: 3px; cursor: pointer;">
+                {% if has_analysis %}Re-analyze{% else %}Analyze{% endif %}
+            </button>
+        </form>
+    </div>
+    {% elif not feedback.content %}
+    <div style="margin: 20px 0; padding: 15px; background: #f8d7da; border-radius: 5px; color: #721c24;">
+        <span style="font-size: 1.2em;">ℹ️</span>
+        <strong>Cannot analyze:</strong> This feedback has no text content (attachments only).
+    </div>
+    {% endif %}
+
     <!-- Original Content -->
     <div style="margin: 30px 0;">
         <h2>Original Feedback</h2>