Resolve canonical public context for any page/widget/chat call.

Transport: the canonical context carries a full location object plus the panchang summary, so the dashboard fetches it on every location change (and it triggers the bundle load). The response is gzip-negotiated via the audited _json_response_maybe_gzip helper — the DECOMPRESSED body is byte-identical to the old return _with_meta(...) path (no contract, field, or value change), and clients that do not advertise Accept-Encoding: gzip (or tiny payloads) get the unchanged JSON body. request is FastAPI-injected, not a query param, so the public query contract (lat/lng/lon/tz/place/date/time) is unchanged. Same proven transport-only pattern as #460/#461/#462/#463/#469/#470/#480.