Broken planes cannot fly; repair heals gradually (ISS-089)

- flyPlane 409s a broken plane (health <= 0) before any refuel math — fuel/cash untouched
- engine auto-chain skips chaining when a landing's wear breaks the plane (queue kept intact)
- finishRepairs heals along round(f x 100) each tick; flip to available at exactly 100 on gate pass
- repairPlane no longer jumps health to 100 — it starts the gradual heal
- REMOVED BROKEN_BURN_MULTIPLIER / conditionBurnMultiplier and all burn sites (unreachable now)
- OpenAPI + route comments reworded; unit tests reworked; e2e maintenance.spec.ts per issue
- v0.45.0

lib/db/schema.ts

@@ -27,7 +27,7 @@ export const planes = sqliteTable('planes', {
   // departureSimTime; on landing the engine auto-chains queue[0] if fuel covers it.
   queue: text('queue').notNull().default('[]'),
   // Structural health in [0, 100] (v0.39.0, ISS-069) — wears down by WEAR_PER_KM per km of
-  // landed legs; at 0 the plane is broken and burns BROKEN_BURN_MULTIPLIER × more fuel.
+  // landed legs; at 0 the plane is broken and cannot fly until repaired (v0.45.0, ISS-089).
   health: real('health').notNull().default(100),
   // Sim-clock epoch ms when an active repair finishes (v0.39.0, ISS-069) — set with status
   // 'repairing', cleared by the engine's flip-back pass; NULL = not in repair.