feat(reader): in-book search for PDFs

PDFs have fully searchable text (pdf.js text layer) — the previous
reflowable-only gate existed only because foliate's generic search
needs DOM documents that PDF sections don't provide. This adds a PDF
pipeline alongside it:

- Fork d065495 exposes the pdf.js document proxy as book.pdf so the
  host can drive text extraction directly.
- New web/src/reader/pdf-search.ts: extractPdfPages() pulls each
  page's textContent with item geometry (progress-reported, cached
  after first search). PDF text items often omit inter-word spaces
  (gaps are positional), so pages are joined gap-aware — baseline
  changes, hasEOL, or horizontal gaps past a font-size threshold
  become spaces — recording a char→item map. searchPdfPages() does
  case-insensitive matching over the joined text and maps each hit
  back to the page-fraction rects of the items it spans, with
  ellipsized pre/match/post excerpts. Pure functions, unit-sanity
  checked (cross-item 'brave new' → two rects).
- runSearch branches: EPUB keeps foliate's DOM search; PDFs search
  the extracted pages, group hits per page ('Page 12'), and render
  on-page hit rectangles through the existing fraction-rect overlay
  (addRectAnnotation) — which re-render automatically when pages
  revisit, same as highlights. Clearing the query removes them.
- Results navigate by page index; the 🔍 button and '/' shortcut now
  appear for PDFs too (comics remain without searchable text).

package.json

@@ -12,7 +12,7 @@
     "dev": "npm run build:ts:dev && npm run build:css"
   },
   "dependencies": {
-    "@bookhoard/foliate-js": "git+https://github.com/john-okeefe/foliate-js.git#1c0ebf3",
+    "@bookhoard/foliate-js": "git+https://github.com/john-okeefe/foliate-js.git#d065495",
     "alpinejs": "^3.15.8",
     "chart.js": "^4.5.1",
     "highlight.js": "^11.11.1",