feat(pdf-server): lazy range-based loading + eager background preloading (#480)

* lazy PDF loading w/ PDFDataRangeTransport

* lint

* feat: lazy PDF loading via range transport + eager background preloading

Replace full-file download with PDFDataRangeTransport so PDF.js fetches
byte ranges on demand. First page renders immediately; remaining pages
load in background for search.

**Range transport (server + client)**
- server.ts: add read_pdf_bytes tool returning base64 chunks with offset
- mcp-app.ts: AppRangeTransport feeds PDF.js via fetchRange/fetchChunk
  with parallel sub-requests for large ranges, Promise-based dedup of
  concurrent requests, and a persistent range cache

**Background preloader**
- Sequential page 1→N text extraction, pauses during interactive
  navigation (preloadPaused flag set in goToPage, cleared in renderPage)
- Debounced live search refresh (500ms) as pages load
- Search UI shows '(loading…)' suffix until all pages processed

**Loading indicators**
- SVG pie in toolbar: fills as pages load, fades on completion,
  turns red on errors with tooltip listing failed pages
- Debounced page-loading overlay (150ms) for uncached page navigation

**Cleanup**
- Remove old full-file chunked download and progress bar
- Remove extractAllPageText (replaced by preloader)
- Remove verbose debug logs (Coverage, RangeReq, cache hit)

examples/pdf-server/tsconfig.json

@@ -6,7 +6,6 @@
     "moduleResolution": "bundler",
     "allowImportingTsExtensions": true,
     "resolveJsonModule": true,
-    "isolatedModules": true,
     "verbatimModuleSyntax": true,
     "noEmit": true,
     "strict": true,