fix(protocol): register all custom scheme privileges in one call

[mrsibe]

What does this PR do?

Fixes the PDF reader, which #131 broke. All custom scheme privileges are now declared by the protocol modules and submitted to Electron in a single registerSchemesAsPrivileged() call.

Why?

protocol.registerSchemesAsPrivileged() replaces the privilege table; it does not append. #131 added a second, separate call:

registerDocumentScheme()      // knownote-doc
registerPdfjsAssetScheme()    // knownote-asset  ← overwrites the table

so knownote-doc lost supportFetchAPI and the renderer's fetch() on it failed:

Fetch API cannot load knownote-doc://docs/doc_...: URL scheme "knownote-doc" is not supported.
Failed to open PDF TypeError: Failed to fetch. URL scheme "knownote-doc" is not supported.

Every PDF failed to open. protocol.handle itself keeps working in the main process without the privilege, which is why nothing else noticed.

The packaged smoke test stayed green because its knownote-doc:// check used the main process (net.fetch), which does not exercise the renderer-facing privilege. That gap is closed here too.

Fixes #135. Regression from #131.

What changed?

• New src/main/protocol/privilegedSchemes.ts: holds declarations, performs the one registerSchemesAsPrivileged() call.
• documentProtocol.ts / pdfjsAssetProtocol.ts: registerXScheme() → declareXScheme(), which only enqueues; no Electron call.
• index.ts: declares both schemes, then calls applyPrivilegedSchemes() once, before the app is ready.
• smokeTest.ts: a new renderer-side fetch of knownote-doc:// (hidden window, intentionally not destroyed — destroying the last window fires window-all-closed and this app closes the database on it).
• test/privilegedSchemes.test.ts: asserts there is exactly one registerSchemesAsPrivileged() call site in src/ and that index.ts declares and submits both schemes.

How was this tested?

• Reproduced the regression and the fix in headless Electron using the repo's real protocol modules:
  • two separate registerSchemesAsPrivileged() calls → knownote-doc:// returns ERR Failed to fetch;
  • one combined call → {"knownote-doc":"ok 15306","knownote-asset":"ok 553"}.
• npm test — 283 pass, 0 fail (2 new).
• npm run typecheck, npm run build — pass.
• npm run build:unpack + smoke:packaged — 22/22 checks pass, including the new knownote-doc:// is fetchable from a renderer (scheme privileges registered).

Screenshots / recordings

Not applicable.

Checklist

• I have reviewed my own changes.
• npm run typecheck passes.
• npm run build passes.
• I have tested the affected user workflow.
• I have not included unrelated changes.
• I have updated documentation when necessary.

Desktop / build changes

• npm run build:unpack passes.
• npm run smoke:packaged passes.