feat(dungeon): boss-fight HUD bar

[silver-snoopy]

What

Gathers the loose top of the boss fight into a single themed HUD bar: back-to-menu door + Floor N/M · <domain> on the left, icon-only SFX/BGM on the right, and the boss name moved just below it.

Design · Plan.

How

• src/ui/bossHud.ts — pure, unit-tested darken(color, factor) + formatRunLabel(campaign, domainShort), and a composer mountBossHud(scene, {boss, campaign, onExit, onBgmToggle}) that draws the bar (darkened environmentColor + subtle border) and reuses mountMenuButton (door) + mountAudioToggles (icon-only).
• src/ui/audioToggles.ts — new iconOnly + y options; the Hub keeps its labeled toggles (passes no iconOnly), so mute/persistence behavior is byte-for-byte unchanged.
• src/ui/inFightNav.ts — mountMenuButton gained an optional position.
• src/types.ts + src/config.ts — domainShort on each boss (Agentic / Claude Code / Prompting / MCP / Context).
• src/scenes/BossFightScene.ts — one mountBossHud(...) call replaces the two separate mounts; boss name y 30 → 66.

Floor = floorsCleared+1 / bossOrder.length; isolated/debug fights (no campaign) gracefully show just the domain.

Tests / checks

• npx vitest run → 127 passing (incl. 7 new: darken, formatRunLabel with/without campaign, and a domainShort-on-every-boss guard).
• tsc --noEmit clean · npm run build clean · root npm run lint (Biome) clean.
• Final review: no Critical/Important issues (audio behavior unchanged, depths/coords sound, floor label matches the on-screen boss, no unused imports).

Manual verification (interactive — not automatable in CI)

At localhost:5173 in a real run, enter a boss fight and confirm:

• Themed bar spans the top; door + Floor 1/5 · <domain> left, icon-only 🔊/🎵 right
• Audio icons still mute and persist across reload; Hub toggles still show labels
• Boss name sits just below the bar, no overlap with bar or question bubble
• Beat a boss → floor number increments next fight
• ?demo shows the bar; a debug-isolated boss shows just the domain (no "Floor"), no crash
• Check 2+ bosses for color cohesion (tune BAR_DARKEN if too dark)

🤖 Generated with Claude Code