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/mcp-app.html

@@ -11,14 +11,6 @@
       <div id="loading" class="loading">
         <div class="spinner"></div>
         <p id="loading-text">Loading PDF...</p>
-        <div
-          id="progress-container"
-          class="progress-container"
-          style="display: none"
-        >
-          <div id="progress-bar" class="progress-bar"></div>
-        </div>
-        <p id="progress-text" class="progress-text"></p>
       </div>
 
       <!-- Error State -->
@@ -33,6 +25,13 @@
         <div class="toolbar">
           <div class="toolbar-left">
             <span id="pdf-title" class="pdf-title">Document</span>
+            <div id="loading-indicator" class="loading-indicator" style="display: none"
+                 title="Loading pages...">
+              <svg viewBox="0 0 20 20" width="14" height="14">
+                <circle class="loading-indicator-bg" cx="10" cy="10" r="8"/>
+                <circle class="loading-indicator-arc" cx="10" cy="10" r="8"/>
+              </svg>
+            </div>
           </div>
           <div class="toolbar-center">
             <button id="prev-btn" class="nav-btn" title="Previous page (←)">