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

app/api/planes/[planeId]/repair/route.ts

@@ -1,10 +1,10 @@
 import { performAction, repairPlane } from '@/lib/game/actions';
 
-// POST /api/planes/:planeId/repair (v0.39.0, ISS-069) — no body. Restores a worn-out plane to
-// full health for the flat REPAIR_COST: it is grounded in "repairing" status until 3 sim days
-// pass, when the engine's tick flips it back to "available". A full-health repair is a free
-// no-op (cost 0). 404 unknown id; 409 plane not grounded or insufficient funds. On success
-// returns the full state snapshot.
+// POST /api/planes/:planeId/repair (v0.39.0, ISS-069) — no body. Grounds a worn-out plane in
+// "repairing" status for the flat REPAIR_COST; its health climbs back to 100 over 3 sim days and
+// the engine's tick flips it to "available" exactly when full (v0.45.0, ISS-089). A full-health
+// repair is a free no-op (cost 0). 404 unknown id; 409 plane not grounded or insufficient funds.
+// On success returns the full state snapshot.
 
 export async function POST(_req: Request, ctx: { params: Promise<{ planeId: string }> }) {
   const { planeId } = await ctx.params;