Simplify school types and persist selected schools

- Add runtime normalization of cryptic school type codes to user-friendly names
  (e.g., AC/ACC/ACCS -> "Academy", CY/CYS -> "Community")
- Update SCHOOL_TYPE_MAP in schemas.py with consolidated mappings
- Add normalize_school_type() and get_school_type_codes_for_filter() helpers
- Persist selected schools in localStorage across page refreshes
- Move "Add to Compare" button from modal footer to header

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/index.html

@@ -330,6 +330,7 @@
                 <h2 id="modal-school-name"></h2>
                 <div class="modal-meta" id="modal-meta"></div>
                 <div class="modal-details" id="modal-details"></div>
+                <button class="btn btn-primary" id="add-to-compare">Add to Compare</button>
             </div>
             <div class="modal-body">
                 <div class="modal-chart-container">
@@ -341,9 +342,6 @@
                     <div class="modal-map" id="modal-map"></div>
                 </div>
             </div>
-            <div class="modal-footer">
-                <button class="btn btn-primary" id="add-to-compare">Add to Compare</button>
-            </div>
         </div>
     </div>