phase 8: Ouroboros boss fight — pattern puzzle with 3 victory paths

First Archon encounter: a cyclical pattern-recognition puzzle.

Boss AI: 4-phase cycle (Coil → Spray → Lash → Digest) with
escalating difficulty (10% faster per cycle, caps at 5 cycles).

Victory paths (all based on real chemistry):
- Chemical: NaOH during Spray phase (acid-base neutralization, 3x dmg)
- Direct: any projectile during Digest vulnerability window
- Catalytic: Hg poison stacks (mercury poisons catalytic sites, reduces
  regen+armor permanently)

New files: src/boss/ (types, ai, victory, arena, factory, reward),
src/data/bosses.json, src/scenes/BossArenaScene.ts, tests/boss.test.ts

Extended: ECS Boss component, CodexEntry 'boss' type, GameScene
triggers arena on Resolution phase completion.

70 new tests (455 total), all passing.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/run/types.ts

@@ -110,7 +110,7 @@ export interface RunDiscoveries {
 
 export interface CodexEntry {
   id: string;
-  type: 'element' | 'reaction' | 'compound' | 'creature';
+  type: 'element' | 'reaction' | 'compound' | 'creature' | 'boss';
   discoveredOnRun: number;
 }