feat: separate AGPL libraries and add dynamic WASM loading

- Add WASM settings page for configuring external AGPL modules
- Implement dynamic loading for PyMuPDF, Ghostscript, and CoherentPDF
- Add Cloudflare Worker proxy for serving WASM files with CORS
- Update all affected tool pages to check WASM availability
- Add showWasmRequiredDialog for missing module configuration

Documentation:
- Update README, licensing.html, and docs to clarify AGPL components
  are not bundled and must be configured separately
- Add WASM-PROXY.md deployment guide with recommended source URLs
- Rename "CPDF" to "CoherentPDF" for consistency

src/pages/pdf-to-pdfa.html

@@ -191,6 +191,29 @@
             </select>
           </div>
 
+          <div
+            class="flex items-center gap-3 bg-gray-700/50 p-4 rounded-lg border border-gray-600"
+          >
+            <input
+              type="checkbox"
+              id="pre-flatten"
+              class="w-5 h-5 text-indigo-600 bg-gray-700 border-gray-600 rounded focus:ring-indigo-500 focus:ring-2"
+            />
+            <div>
+              <label
+                for="pre-flatten"
+                class="text-sm font-medium text-gray-200 cursor-pointer"
+              >
+                Pre-flatten PDF (recommended for complex files)
+              </label>
+              <p class="text-xs text-gray-400 mt-1">
+                Converts the PDF to images first, ensuring better PDF/A
+                compliance. Recommended if validation fails on the normal
+                conversion.
+              </p>
+            </div>
+          </div>
+
           <button id="process-btn" class="btn-gradient w-full mt-4">
             Convert to PDF/A
           </button>