feat(input): scroll-wheel zoom, click binds and safe keybind rules (#285)

[Maxaubert]

Closes #285.

What

• Scroll-wheel zoom: hold the chosen modifiers (never Ctrl or Shift alone) and turn the wheel. A notch zooms as far as holding the bind does in 0.1 s at the same speed slider (zoomInSpeed up, zoomOutSpeed down), so about 10 notches a second feels like holding. No separate step setting.
• Click binds: left/right/middle click with modifiers; side buttons can carry modifiers too.
• One safety rule set (src/keybind_rules.h, mirrored in ui/src/lib/keybindRules.js, both tested against one fixture): typing keys alone, Shift/AltGr + a typing key, Windows-reserved combos and Win shortcuts are refused with a reason. Stored binds the rules refuse are reset once, with a notice in Settings.
• Alt/Win combos inject one mask key so Start and app menu bars do not activate.
• A key bind is swallowed only with its modifiers held (Ctrl+F1 leaves a plain F1 alone).
• The native Magnifier model passes each wheel notch on.

Review

A 4-area review with adversarial verification confirmed 8 findings; all fixed in 8ff5966.

Verified

• 360 unit tests on the branch, 379 on the combined build; 70/72 Playwright tests.
• Live on the owner's PC (signed UIAccess build, SendInput): Ctrl+Alt+wheel x3 at speed 2.7 -> 4.07x with no app scroll; plain and Ctrl wheel reach the app; Ctrl+Alt+left held zooms and the app gets no click; Win+PageUp zooms without opening Start; Alt+PageDown zooms out without activating the menu bar; plain PageUp/PageDown reach the app.
• Not live-tested: the raw-input net for a lost click UP (needs a hook eviction), and the native Magnifier wheel path.

Notes

• Version 0.13.0 (owner decision). The colour-filter PR (Colour filters: invert, greyscale, high contrast, custom tints #288) bumps past it when it merges.
• Release is unsigned (per-machine local signing in setup, as before).

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