P20-T02 — Explore city and fuel journey

Status: LOCAL_DONE on codex/phase-20-community-discovery. Issue: #77. Binds B-BR-C01/C06 and BUC-C01 to existing contracts. No backend, map or new index in this task.

What already existed (reused, not rebuilt)

• Manual city via preferred location header (SelectLocationUseCase.getPreferredLocation, no GPS required).
• Fuel filter chips (FuelProduct.entries) with SavedStateHandle persistence.
• Price-ascending sort (StationPriceOrderingRule, GetStationPricesUseCase UC-007).
• Offline banner + cached ANP reads, download prompt, BR-010 empty state, route action.
• Guest access: no signup gate on this journey.

What this task adds

• Domain DiscoveryStationsRule (pure): station-name search over trade/legal name, brand and address (case-insensitive; blank or below-minimum-length typing does not exclude; committed queries still enforce >= 2 chars via DiscoveryQuery), PRICE_ASC / RECENCY_DESC (unknown dates last, price tie-break), paginate with hasMore/totalCount and 1..100 page-size bounds. No match is an honest empty list.
• StationsViewModel: searchQuery state persisted in SavedStateHandle, local filtering over the cached domain list without reload; failed refresh keeps the last good list and shows the error above it instead of replacing it; explicit fuel change still drops the previous fuel's cache.
• StationsScreen: station-name search field; cached list stays visible during reload/failed refresh with retry; explicit no-match copy (stations_search_no_match, en + pt-BR, other locales fall back to en).

Explicitly deferred (not waived)

• Optional map: only after a provider/dependency/privacy audit, per frozen IA.
• RECENCY_DESC list toggle and backend paginated endpoint: rule-level only until measured fixture scale justifies an index (P20-T01 note).

Validation

• DiscoveryStationsRuleTest 7/0-fail (RED compile-fail → GREEN).
• StationsViewModelTest 7/0-fail (2 new: failed-refresh cache, local search).
• ./gradlew :domain:test, :app:testDebugUnitTest, :app:assembleDebug (affected suites).
• git diff --check clean; scoped secret review (no secrets/PII/GPS/photo content).