fix(server): declare Allow: GET on the new 405 responses

RFC 9110 section 15.5.6 requires a 405 to name the methods it accepts, and
/api/radio/stations already does this in-tree. Thanks to kvnloo for catching it
on review. The same gap on the pre-existing handlers is tracked in #809 and is
deliberately left alone here.

docs/CURRENT-STATE.md

@@ -4072,7 +4072,7 @@ are omitted rather than framing the wrong part of the globe.
 - `/api/overpass` is bounded by body/response caps, per-client/global rate limits, concurrency limits, operator-configured upstreams, in-flight dedupe, cache bounds, and static validation that every selector is spatially bounded.
 - `/api/military-installations` uses an independent limiter with the same 90-per-client/300-global one-minute bounds, so viewport installation refreshes never consume `/api/overpass` annotation capacity.
 - `/api/route` proxies bounded OSRM route requests for annotation routes, with profile allowlisting, distance caps, response caps, caching, and sanitized "no route found" errors.
-- `/api/opensky`, `/api/adsblol/mil`, and `/api/route` are read-only query proxies and answer `405 Method Not Allowed` to anything but `GET`, as `/api/geocode` and the other query proxies already did. The refusal precedes rate limiting and any upstream call.
+- `/api/opensky`, `/api/adsblol/mil`, and `/api/route` are read-only query proxies and answer `405 Method Not Allowed` to anything but `GET`, as `/api/geocode` and the other query proxies already did, declaring `Allow: GET` with it as `/api/radio/stations` does. The refusal precedes rate limiting and any upstream call.
 - Track endpoints: `/api/ais-live/track?mmsi=` (server-accumulated ring buffers; sub-route handled before the rows snapshot), `/api/opensky-track?icao24=` (OAuth, 60s cache, sanitized errors, independent OpenSky credit bucket), `/api/adsblol/trace?hex=` (60s cache, 5MB cap, ODbL attribution required in UI).
 - Realtime debug logs redact API keys, bearer tokens, client secrets, and image data URLs before writing to disk; request bodies are size-capped.
 - `/api/realtime/debug-log` enforces an always-on 120-per-client/400-global one-minute limiter (not the opt-in `GEV_RATELIMIT_OPENAI_PER_MIN` bucket the cost-bearing OpenAI routes share), appends asynchronously through a serialized queue, and rotates `realtime-conversations.jsonl` at 32 MB keeping one prior generation, so the sink is bounded at twice that regardless of session length. A malformed record answers 400 and a failed write 500, both with a fixed message.