WCAG accessibility support (a11y phase 1 + 2)

[McSpace]

Summary

Adds WCAG/accessibility support to the seatmap (opt-in via wcag config). Unit 598/598, e2e 123/123 (against the WCAG demo).

Highlights

• Grid semantics + roving tabindex; arrow-key seat navigation (skips aisles/empties); arrow keys remap to on-screen direction in horizontal mode (P1a).
• Tooltip-as-dialog keyboard ownership (focus trapped, Escape closes); visible focus rings.
• Accessible list view (row numbers, conditional columns, position dropdown, merged status+price action button).
• Skip-link handling; landmark/labelling fixes; colour-contrast pass.
• Includes the horizontal React-parity layout work as its base.

Test plan

• Unit: npx ng test seatmap-lib --watch=false → 598/598.
• e2e (a11y + axe + full suite) against the WCAG demo → 123/123.

⚠️ Merge order / reconciliation

• This branch shares the horizontal-layout base with PR React parity: horizontal layout + seat colouring #22 (dev → main) but predates that PR's seat-colour React-parity refactor. It still contains the old colorfulSeatsByScore / colorfulSeatsByClass flags + color-tint.ts, which React parity: horizontal layout + seat colouring #22 removes.
• Recommended: merge React parity: horizontal layout + seat colouring #22 first, then reconcile this branch with main (drop the old colour flags / re-apply the seat-colour refactor) before merging, so the removed flags are not reintroduced.

🤖 Generated with Claude Code

[nexus]

hi @McSpace ,
Please fix github-advanced-security [bot] findings and also, please pay attention to the following points:

[
  {
    "file": "projects/seatmap-lib/src/lib/components/jets-plane-body/jets-plane-body.component.ts",
    "line": 174,
    "summary": "fuselageFill getter dropped the hullColor fallback — consumers using the still-public hullColor alias now get default grey fuselage instead of their branded color.",
    "failure_scenario": "Old getter: `hullColor ?? fuselageFillColor ?? default`. New getter: `fuselageFillColor ?? default`. IColorTheme.hullColor is still declared in types.ts (line 93, marked @deprecated but not removed). Wings still fall back to hullColor correctly — so a consumer with `colorTheme: { hullColor: '#002244' }` would see branded navy wings but default grey fuselage, a visible mismatch."
  },
  {
    "file": "projects/seatmap-lib/src/lib/components/jets-seat-map/jets-seat-map.component.ts",
    "line": 1005,
    "summary": "onGridFocusin always records focusedCell.deckIdx = activeDeckIndex, ignoring which physical deck the focused seat belongs to when singleDeckMode=false.",
    "failure_scenario": "With singleDeckMode=false (valid config, tested in spec) all decks are rendered simultaneously. User Tab-focuses a seat in deck 1 while activeDeckIndex=0 → focusedCell.deckIdx=0 recorded → SeatGridNavigationService.move() does `decks[0].rows` → arrow navigation jumps to a seat in the wrong deck. The correct deck index is available in the DOM via `[attr.data-deck-index]` on the ancestor deck-wrapper but is never read."
  },
  {
    "file": "projects/seatmap-lib/src/lib/components/jets-seat-map/jets-seat-map.component.ts",
    "line": 1552,
    "summary": "_prepareSeatForEmit casts a formatted price string (e.g. 'USD 29') to number via `as unknown as number`, making seat.price a string at runtime while the type says number|string.",
    "failure_scenario": "priceStr is built as `` `${currency} ${numericPrice}` `` (e.g. 'USD 29') then emitted as `price: priceStr as unknown as number`. Any integrator doing `if (seat.price > 0)` or `seat.price * quantity` gets NaN. The raw numeric value is available in the separate `priceValue` field added in this PR, but nothing in the type signature directs consumers toward it."
  },
  {
    "file": "projects/seatmap-lib/src/lib/components/jets-seat-map/jets-seat-map.component.ts",
    "line": 590,
    "summary": "getDeckFloorLiningWidth mixes coordinate spaces — subtracts unscaled fuselageStrokeWidth from a scaled pixel width, producing a lining that is slightly wrong at non-default displayScale values.",
    "failure_scenario": "Line 590: `const innerW = this.fuselageBodyWidth - 2 * stroke` where fuselageBodyWidth is in scaled CSS pixels but stroke is the raw config value. The CSS border is `stroke * displayScale` (correctly scaled in jets-plane-body). The mismatch introduces an error of `2 * stroke * (displayScale - 1)` in innerW — typically a few pixels at displayScale < 1, causing the lining to slightly overflow the fuselage outline. Fix: use `2 * stroke * this.displayScale` on line 590."
  }
]

[McSpace]

Fixed all four review findings and the three CodeQL alerts (#42/#43/#44) in 09529cb. build:lib is green and 588/588 unit tests pass.