feat: show recent files with font previews in the launcher

[kostyafarber]

Summary

• The launcher is rebuilt around recent files: a centred lockup, then a Recent header with New Font ⌘N (primary), Open Font… ⌘O, and a grid/list toggle. It opens as a 960×720 window (capped to 90% of smaller screens) and appears only once its recent files have rendered; the lockup and header sit at a fixed position so switching views never moves them.
• Grid cards show a specimen drawn from the font, the filename (middle-truncated so the extension stays visible), and when it was opened; list rows add a specimen chip and the full path. Hovering reveals a ⋯ menu with Reveal in Finder, Copy Path, and Remove from Recents (with undo). Missing files are dimmed and offer Locate… and Remove.
• File → Open Recent lists the same files and has Clear Menu.
• Recents live in main (recent-documents.json in userData, capped at 20), keyed by DocumentId with a canonical-path fallback, and are recorded on every open, Save As, and preview conversion. Updates are held back from the launcher while a font opens, so it never shows a half-ready card.
• New shift-specimen crate: picks the specimen from the compiled font (symbol glyphs → declared non-Latin dlng languages → Ag → script pair → AG/ag → first drawn glyphs), shapes it with HarfRust at the default location, and returns SVG path data fitted to the ink. .shift documents and sources compile through the existing fontc exporter (FontExporter::compile_ttf); binaries are read as they are.
• Specimens are built in the session's utility process after an open (when missing or stale) and after each save, then cached per file with a rules revision. The launcher never opens fonts.
• Shared UI: ToggleGroup/Toggle, a strong Separator variant, Select options that align and don't wrap, and an on-accent theme token so primary buttons stay readable on pale accents (e.g. Dracula).

Issue

Closes #467

Testing

• pnpm check (lint, typecheck, desktop unit tests)
• Pre-commit hooks: cargo check, fmt, clippy, cargo test, oxlint, tsgo, vitest, dead-code, sdk API report
• cargo test -p shift-specimen — rule selection, dlng parsing, viewport fitting
• Specimen choice spot-checked through the native addon against real fonts: SF Arabic → حب, SF Hebrew → אב, AppleGothic → 한, Ayuthaya → กข, Georgia / New York / Open Sans → Ag, MutatorSans → AG, Homenaje.glyphs (compiled from source) → Ag, symbol fonts → first drawn glyphs
• Manually verified in the running app in light and dark themes: grid, specimens, ⋯ menu, New font, Open Font…
• E2E not run locally: new e2e/recent-files.spec.ts (platform project) covers reopen-from-card after relaunch, specimen text, remove + undo, and Open Recent + Clear Menu; existing specs and fixtures now use the "New Font" and "Open Font…" buttons
• landing-default.png will fail until regenerated with ci: update visual snapshots

Follow-up

• Stale specimens (after a rules revision bump, or for fonts never reopened) only rebuild on the next open; building them in the background on launcher start is not in this PR.
• fontc does not write meta dlng, so compiled documents and sources always take the Ag-first path.

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