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

public/workers/add-attachments.worker.d.ts

@@ -5,6 +5,7 @@ interface AddAttachmentsMessage {
   pdfBuffer: ArrayBuffer;
   attachmentBuffers: ArrayBuffer[];
   attachmentNames: string[];
+  cpdfUrl?: string;
 }
 
 interface AddAttachmentsSuccessResponse {
@@ -17,4 +18,6 @@ interface AddAttachmentsErrorResponse {
   message: string;
 }
 
-type AddAttachmentsResponse = AddAttachmentsSuccessResponse | AddAttachmentsErrorResponse;
+type AddAttachmentsResponse =
+  | AddAttachmentsSuccessResponse
+  | AddAttachmentsErrorResponse;