fix(mobile): allow selecting PDF text layer

[codedogQBY]

Analysis

• Mobile PDF pages render as fixed-layout iframes with a canvas, a PDF.js text layer, and an annotation layer.
• The canvas/annotation layer could win touch hit-testing over the transparent text layer, while the PDF text layer also defaulted to panning-oriented cursor/gesture behavior.
• For PDFs that contain an actual text layer, Android long-press selection should hit the text spans so the existing ReadAny selection popover can copy the text. Image-only scanned PDFs still do not expose selectable text without OCR.

Changes

• Detect PDF text-layer documents in the mobile reader template.
• Disable pointer events/user selection on the PDF canvas so it does not consume text gestures.
• Promote .textLayer and its spans as selectable touch targets, while keeping PDF link annotations clickable.
• Rebuilt packages/app-expo/assets/reader/reader.html from the template.

Verification

• pnpm --filter @readany/app-expo run build:reader
• git diff --check
• rg -n "isPdfTextLayerDoc|getPdfTextSelectionStyles|annotationLayer section|#canvas, #canvas canvas|touch-action: auto" packages/app-expo/assets/reader/reader.template.html packages/app-expo/assets/reader/reader.html

Note: pnpm exec biome check packages/app-expo/scripts/build-reader.js still reports pre-existing style issues in the build script (node: protocol and template-string suggestions); this PR does not touch that script.

Fixes #362