feat(search): Add complete Search UI with API and web interface

Implements full search functionality for StarPunk v1.1.0.

Search API Endpoint (/api/search):
- GET endpoint with query parameter (q) validation
- Pagination via limit (default 20, max 100) and offset parameters
- JSON response with results count and formatted search results
- Authentication-aware: anonymous users see published notes only
- Graceful handling of FTS5 unavailability (503 error)
- Proper error responses for missing/empty queries

Search Web Interface (/search):
- HTML search results page with Bootstrap-inspired styling
- Search form with HTML5 validation (minlength=2, maxlength=100)
- Results display with title, excerpt, date, and links
- Empty state for no results
- Error state for FTS5 unavailability
- Simple pagination (Next/Previous navigation)

Navigation Integration:
- Added search box to site navigation in base.html
- Preserves query parameter on results page
- Responsive design with emoji search icon
- Accessible with proper ARIA labels

FTS Index Population:
- Added startup check in __init__.py for empty FTS index
- Automatic rebuild from existing notes on first run
- Graceful degradation if population fails
- Logging for troubleshooting

Security Features:
- XSS prevention: HTML in search results properly escaped
- Safe highlighting: FTS5 <mark> tags preserved, user content escaped
- Query validation: empty queries rejected, length limits enforced
- SQL injection prevention via FTS5 query parser
- Authentication filtering: unpublished notes hidden from anonymous users

Testing:
- Added 41 comprehensive tests across 3 test files
- test_search_api.py: 12 tests for API endpoint validation
- test_search_integration.py: 17 tests for UI rendering and integration
- test_search_security.py: 12 tests for XSS, SQL injection, auth filtering
- All tests passing with no regressions

Implementation follows architect specifications from:
- docs/architecture/v1.1.0-validation-report.md
- docs/architecture/v1.1.0-feature-architecture.md
- docs/decisions/ADR-034-full-text-search.md

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

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

templates/base.html

@@ -24,6 +24,20 @@
       {% if g.me %}
       <a href="{{ url_for('admin.dashboard') }}">Admin</a>
       {% endif %}
+      <form action="/search" method="get" role="search" style="margin-left: auto; display: flex; gap: var(--spacing-sm);">
+        <input
+          type="search"
+          name="q"
+          placeholder="Search..."
+          aria-label="Search"
+          value="{{ request.args.get('q', '') }}"
+          minlength="2"
+          maxlength="100"
+          required
+          style="width: 200px; padding: var(--spacing-xs) var(--spacing-sm);"
+        >
+        <button type="submit" class="button button-small" style="padding: var(--spacing-xs) var(--spacing-sm);">🔍</button>
+      </form>
     </nav>
   </header>