feat(view): Explorer-style view sizes with Ctrl+scroll

[Maxaubert]

Closes #36.

Implements concept 04 from docs/mockups/view-zoom (spec docs/superpowers/specs/2026-10-05-view-sizes-design.md, plan docs/superpowers/plans/2026-10-05-view-sizes.md).

• Six sizes for the files view: Details (the table), Large details (the same table with 44px rows, a 32px thumb and 14px names), Tiles, Medium icons, Large icons, Extra large icons.
• Ctrl+wheel over the files view steps one size per notch (trackpads: a step per 40px); nothing happens over the inspector or sidebar, and the page never zooms.
• Ctrl+= / Ctrl+- step, Ctrl+0 resets to Details, Ctrl+Shift+1..6 jump. Shortcuts are ignored while a dialog is open.
• A View button in the toolbar shows the current size and opens a menu with the sizes and shortcuts.
• The size is remembered. Selection, the right-click menu, double-click, arrow-key grid navigation, group headers and running/done/failed states work in every size.
• Sharp thumbnails on high-DPI screens: the bucket (128/256/512/768/1024) follows the view size and devicePixelRatio and updates when the window moves to another monitor. Cards get cover thumbnails (the short side reaches the bucket), cached per path and bucket; stepping back down reuses a bigger cached one. In main, when the Windows shell returns a smaller image than asked (it often stops at 256), magick/ffmpeg render the thumbnail instead, never upscaling the source.
• Version 0.7.0.

Verification

• npm test 852 passed (1 skipped), typecheck, lint, prettier, build, npm run test:e2e 76 passed, 2 skipped (the opt-in shots), incl. both GPU tests and 8 view-size tests (Large details geometry, thumbnails really reach 768).
• At DPR 2.25 (--force-device-scale-factor=2.25), thumbnail naturalWidth x naturalHeight for a 3000x2000 PNG / a 1920x1080 MP4: Details, Large details, Tiles 128x86 / 128x72; Medium and Large 768x512 / 910x512 (512 bucket); Extra large 1152x768 / 1365x768 (768 bucket).
• Scripted checks in the built app: wheel steps, inspector ignored, Ctrl+Shift+3, View menu, persistence after reload, multi-select + right-click + double-click in a grid.
• Screenshots: docs/mockups/view-zoom/shots/impl-size0..5.png (impl-size1 = Large details) and impl-menu.png next to the mockup shots.
• Installed 0.7.0 locally.

Note: once anything is selected, every card shows its checkbox (spec 4 and the mockup's own rule).

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