Restructure repository and implement secure search feature

Phase 1: Consolidate shared infrastructure
- Create shared/ directory for common code
- Consolidate Database.php from front-backend and formulaire into unified shared/Database.php
  - Smart path detection for test.db vs posterg.db
  - Secure search with wildcard escaping and input validation
  - Support both singleton and direct instantiation patterns
  - Full CRUD methods for admin functionality
- Move RateLimit.php to shared/ (30 requests/min)
- Update all require paths across apps to use shared/

Phase 2: Reorganize directory structure
- Rename front-backend/ → apps/public/
- Rename formulaire/ → apps/admin/
- Rename db/ → database/
- Update all file paths for new structure
- Create root .gitignore excluding databases, cache, logs

Implement secure search feature
- Add apps/public/search.php with full-text search across theses
- Search filters: query, year, orientation, AP program, keywords
- Security features:
  - SQL injection prevention (prepared statements)
  - Wildcard injection prevention (escape % and _)
  - Input validation (max 200 chars, year range 1900-2100)
  - Rate limiting (30 req/min per IP)
  - Pagination limited to 100 results/page
  - XSS protection (htmlspecialchars on output)

Add comprehensive test suite
- Create apps/public/tests/ with proper structure
  - tests/Integration/SearchTest.php - 12 search scenarios
  - tests/Security/SecurityTest.php - vulnerability testing
  - tests/Unit/RateLimitTest.php - rate limit behavior
- Create database/fixtures/CreateTestDatabase.php
- Add apps/public/run-tests.php test runner
- All tests passing (4/4 suites)

Update deployment configuration
- Rename justfile 'sync' recipe to 'deploy'
- Create deploy group with separate deploy-public and deploy-admin
- Add test-deploy recipe for test database
- Exclude *.db, tests/, cache/, *.md from production deploy
- Deploy shared/ to both public and admin locations

Stats: +4482 insertions, -654 deletions across 72 files

apps/admin/assets/icon.svg

@@ -0,0 +1,65 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   width="24"
+   height="24"
+   viewBox="0 0 24 24"
+   fill="none"
+   stroke="currentColor"
+   stroke-width="2"
+   stroke-linecap="round"
+   stroke-linejoin="round"
+   class="lucide lucide-archive-restore"
+   version="1.1"
+   id="svg12"
+   sodipodi:docname="icon.svg"
+   inkscape:version="1.2.2 (b0a8486541, 2022-12-01)"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:svg="http://www.w3.org/2000/svg">
+  <defs
+     id="defs16" />
+  <sodipodi:namedview
+     id="namedview14"
+     pagecolor="#ffffff"
+     bordercolor="#000000"
+     borderopacity="0.25"
+     inkscape:showpageshadow="2"
+     inkscape:pageopacity="0.0"
+     inkscape:pagecheckerboard="0"
+     inkscape:deskcolor="#d1d1d1"
+     showgrid="false"
+     inkscape:zoom="24.719275"
+     inkscape:cx="5.2185997"
+     inkscape:cy="13.713995"
+     inkscape:window-width="1920"
+     inkscape:window-height="1011"
+     inkscape:window-x="0"
+     inkscape:window-y="32"
+     inkscape:window-maximized="1"
+     inkscape:current-layer="svg12" />
+  <rect
+     width="20"
+     height="5"
+     x="2"
+     y="4"
+     rx="2"
+     id="rect2"
+     style="stroke:#c104fc;stroke-opacity:1" />
+  <path
+     d="M12 13v7"
+     id="path4"
+     style="stroke:#c104fc;stroke-opacity:1" />
+  <path
+     d="m9 16 3-3 3 3"
+     id="path6"
+     style="stroke:#c104fc;stroke-opacity:1" />
+  <path
+     d="M4 9v9a2 2 0 0 0 2 2h2"
+     id="path8"
+     style="stroke:#c104fc;stroke-opacity:1" />
+  <path
+     d="M20 9v9a2 2 0 0 1-2 2h-2"
+     id="path10"
+     style="stroke:#c104fc;stroke-opacity:1" />
+</svg>