feat(desktop/pdf): fit-page, 90° rotation + hand/pan tool, ink-drag canvas preview (#321)

[agentfleets]

Closes #321

Implements the last remaining tail of the PDF reader polish issue — the two items left open in the issue comments (fit-page mode + rotation + hand/pan tool; ink-drag preview re-rendering the whole page per pointermove).

What

Fit-page + rotation + hand/pan (PdfCanvas.tsx)

• Fit-page button alongside the existing fit-width: computes the scale that fits the whole page (both axes) into the scroll viewport; the resulting scale persists via the existing PDF_SCALE_KEY mechanism.
• 90°-step rotation toolbar button, persisted (termipod.pdf.rotation, same shared-across-PDFs pattern as zoom). User rotation stacks on the page's own (page.rotate + rotation) for canvas/text/link rendering; the pre-measured page footprints just swap axes at 90°/270° (no re-measure); render-task cancellation and live-DPR re-rasterization are unchanged. Annotation overlays, creation hit-mapping (note/area/ink/text-selection), area-screenshot capture, and annotation/dest jump offsets all map through rotation-aware pdfPtToView/viewToPdfPt helpers — rotation 0 degenerates to the old multiply + y-flip, so stored annotations are unaffected. Thumbnails rotate with the pages.
• Hand/pan tool: drag anywhere in the scroll view to pan (grab/grabbing cursors, text selection disabled while armed); window listeners instead of setPointerCapture (WebView2), and the trailing click after a drag is swallowed so a pan released over a link doesn't open it.
• New toolbar labels/tooltips localized en + zh (read.zoomFitPage, read.rotateCw, read.panTool); three new stroke icons (fit-page, rotate-cw, hand).

Ink-drag preview

• The in-progress ink stroke now draws into a lightweight DPR-scaled canvas overlay (ref-only, incremental lineTo per move) instead of a draft state that re-rendered the whole page component on every pointermove. React state (the annotation store) is touched once, on pointer-up. The area-rect draft preview is unchanged.

Why

• These were the only two open items left on the issue after the earlier shipped passes (match-granular search, load progress, zoom persistence, live-DPR, popover clamp, ArtifactViewer PdfCanvas, EPUB themes).

How verified

• npm run build (sync:tokens + tsc --noEmit + vite build) — green.
• scripts/lint-desktop-tokens.sh — clean (no new hex/primitive/phantom tokens; hand-tool CSS uses cursor/user-select only).
• Rotation geometry (pdfPtToView/viewToPdfPt) round-trip-tested for 0/90/180/270 incl. corner expectations; rotation-0 output verified identical to the previous mapping.
• No Rust changes; no package.json/lockfile changes.

[physercoe]

APPROVE. Rotation × annotation geometry verified correct against pdf.js viewport math for all four rotations (pdfPtToView/viewToPdfPt inverse pair; rotation-0 byte-identical so existing anchors unaffected). Ink preview is ref-only until pointer-up; hand/pan tracks via window listeners (WebView2 lesson). Rebased onto main and resolved the PdfCanvas drilled-t→local-useT() merge (kept #321 rot, dropped the t prop to match main). Cosmetic minor: ToC/internal-link jump lands page-top while rotated (goToAnnotation is correct).

[physercoe]

Re-approve after rebasing onto main (incl #342). Resolved the #342×#344 overlap in PdfCanvas by taking the union — kept both #316 toolTitle + tool-shortcut effect and #321 rotation-aware annoAnchor, dropped the superseded annoTopY. Clean tsc+vite build and token lint.