fix(tray): scale auto-fit measure by active zoom + clamp proof anchor (#265)

[Finesssee]

Fixes the two tray-layout bugs from #265 (surfaced by the #261 repro rig).

1. useTrayPanelLayout measure vs CSS zoom

TrayPanel renders the surface with zoom: trayScale, but every DOM metric the auto-fit pass reads — scrollHeight and bounding rects — is reported in the surface's local, pre-zoom px (measured identical at 100/150/200% in the 261 probes). The WIN32 window was sized to the pre-zoom height, so at >100% tall cards clipped below the fold.

• New exported helper scaledContentHeight(rawHeight, zoom) in useTrayPanelLayout.ts: identity for zoom invalid/≤0/1, else Math.round(raw * zoom). Applied at both measure derivations — the scrollHeight/rect-height seed and the bottom-edge walk — before the existing [minHeight, maxHeight] clamp. The +4px fudge, clamp semantics, and the 2px shouldResize threshold are unchanged.
• useTrayPanelController passes the already-computed trayScale as the hook's new zoom option; layoutKey already includes trayScaleDraft, so zoom changes re-trigger the layout pass.
• Horizontal-scrollbar follow-up: .menu-surface's min-width: 260px is interpreted in zoom-local px (renders 390px at 150% inside the 328px window → document-level h-scrollbar + right-clipped content). Re-asserted min-width: 0 in the existing cascade-order .menu-surface--tray override block (the tray window's own 300px min covers the floor).

Test (TrayPanel.test.tsx, "scales the auto-fit measure by the active tray zoom before clamping (#265)"): pinned scrollHeight 505 at trayScalePercent: 150 commits 328×762 (round(505×1.5)+4); 700 clamps to the mocked work-area cap 884. Mutation-checked (fails without scaling).

2. Proof-harness anchor overflows work area

The harness anchored the panel once at the default initial size (y=252 on 1920×1080) and never re-anchors; a tall auto-fit settle pushed the bottom edge below the 1040px work bottom. (set_max_size was tried first and is ignored by Win32 for programmatic setSize.)

• proof_harness.rs: proof_window_position now wraps the raw anchor with proof_anchor_y(anchor, work_bottom, max_settle) = anchor.min(work_bottom - 8 - max_settle), where max settle mirrors the frontend's 920px auto-fit cap. Anchors that already fit are unchanged; overflowing ones move up just enough that even the capped settle's bottom edge stays at work_bottom - 8.

Test (proof_harness::tests::tall_panel_bottom_edge_never_passes_work_bottom_minus_inset): 252 → justified 112 on the 1080 rig; settled 920 bottoms exactly at 1032; short settles stay on screen; tall-display anchors unchanged.

Gates (run against the committed tree in a pristine worktree)

• pnpm --dir apps/desktop-tauri exec tsc --noEmit ok; pnpm --dir apps/desktop-tauri test — 227 passed
• cargo test --manifest-path apps/desktop-tauri/src-tauri/Cargo.toml — 332 passed; cargo clippy --all-targets -- -D warnings ok; cargo fmt --all ok

Live CUA verification (150% zoom, seeded tall Codex card)

Tray zoom driven to 150% through the panel footer Zoom slider via CDP (UIA ValuePattern is ignored by WebView2; the slider's real React onChange path was dispatched) — persisted trayScalePercent: 150 confirmed via get_settings_snapshot, applied CSS zoom: 1.5 confirmed. Relaunched CODEXBAR_PROOF_MODE=trayPanel with CODEXBAR_SEED_USAGE_JSON (proof-261-seed/full shape, timestamps freshened).

Observed (1920×1080, work area 1920×1040):

• Settled window rect (1580, 112, 328, 920) → bottom edge 1032 = workBottom 1040 − 8 inset (pre-fix: anchored at y=252, short or overflowing).
• DOM: bodyScrollWidth == clientWidth == 328 → no horizontal overflow/scrollbar; footer (Quit row) fully visible (footer.bottom 841 ≤ innerHeight 920) — the card's bottom content is on screen (previously clipped).
• Artifacts: proof-265/zoom150-tallcard-fixed.png, proof-265/zoom150-tallcard-fixed-rects.json, proof-265/zoom150-tallcard-fixed-observation.json.

Closes #265

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