Replace 2GIS MapKit with OpenStreetMap (osmdroid) — no key needed

Getting a working mobile-SDK key from 2GIS turned out to require a
sales-mediated B2B process (Platform Manager subscription, demo keys
explicitly excluded from mobile SDK use per their own docs), not a
quick self-serve signup. Swapped to osmdroid instead: free, no API
key or account, works immediately.

CityMapView (replacing DgisMapView/DgisSdkProvider) wraps osmdroid's
View-based MapView via AndroidView, forwarding lifecycle events, with
markers for the user's location and each nearby place. Configured
required OSM tile-usage-policy user agent + app-private tile cache in
GuideCityApp. Removed the now-unused DGIS_API_KEY plumbing and the
arm64-only ABI filter (osmdroid has no heavy native libs, so it's not
needed) — APK is back down to ~19.6MB from ~69MB.

Verified: testDebugUnitTest passes, assembleDebug produces a working
APK, sent via the Telegram bot (previously blocked by its 50MB limit
with the 2GIS build).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -9,7 +9,7 @@ voice while showing a swipeable card stack. Starting city: Moscow.
 ```
                  ┌────────────────────┐
                  │   Android app      │  Kotlin + Jetpack Compose
-                 │  (android/)        │  2GIS map, on-device TTS,
+                 │  (android/)        │  OSM map, on-device TTS,
                  └─────────┬──────────┘  location, Room favorites
                            │ HTTPS / REST (JSON)
                  ┌─────────▼──────────┐
@@ -25,7 +25,7 @@ voice while showing a swipeable card stack. Starting city: Moscow.
 - `backend/` — FastAPI service exposing city/place/nearby-search endpoints,
   backed by PostgreSQL+PostGIS. See `backend/` for details.
 - `android/` — Kotlin/Compose app skeleton (MVVM, Hilt, Retrofit, Room,
-  DataStore, 2GIS MapKit, on-device TextToSpeech).
+  DataStore, OpenStreetMap via osmdroid, on-device TextToSpeech).
 
 ## Backend quickstart
 
@@ -56,7 +56,7 @@ which works from anywhere (not just the local network) and is the preferred
 
 ```bash
 cp android/local.properties.example android/local.properties
-# fill in sdk.dir and DGIS_API_KEY (test key: b4df01a8-61db-4cb9-8286-7e069495987d)
+# fill in sdk.dir (and API_BASE_URL if not using the default)
 cd android && ./gradlew :app:assembleDebug
 ```
 
@@ -68,39 +68,18 @@ Wi-Fi/LAN.
 Run unit tests before building — `./gradlew testDebugUnitTest`, then
 `./gradlew :app:assembleDebug`.
 
-## 2GIS map SDK
+## Map
 
-The app depends on the real 2GIS MapKit SDK (`ru.dgis.sdk:sdk-map` +
-`compose-map`, from `https://artifactory.2gis.dev/sdk-maven-release`, wired
-up in `settings.gradle.kts`/`app/build.gradle.kts`). It needs a **separate**
-key from the `DGIS_API_KEY` above:
-
-- `DGIS_API_KEY` (the `b4df01a...` value) is a 2GIS **public REST/JS API**
-  key — not used by the native SDK at all currently.
-- The native MapKit SDK instead needs a **`dgissdk.key` file**, issued
-  per-app (tied to the package name `com.guidecity.app`) from
-  https://dev.2gis.com/. Place it at `android/app/src/main/assets/dgissdk.key`
-  (gitignored — don't commit it).
-
-Without that key file, `DgisSdkProvider` fails to initialize (logged, not
-crashed) and `DgisMapView` falls back to a placeholder canvas rendering
-(user location + nearby place dots, no real map tiles). Once a real key is
-in place, the real map should render automatically — no code changes needed.
-
-Also note: the SDK bundles native libraries per CPU architecture, which
-balloons APK size a lot (~19MB → ~190MB unfiltered). `app/build.gradle.kts`
-restricts `ndk.abiFilters` to `arm64-v8a` only (~69MB) since that covers
-virtually all real devices today — remove that filter if you need to test
-on an x86 emulator or 32-bit device.
+Uses OpenStreetMap tiles via [osmdroid](https://github.com/osmdroid/osmdroid)
+(`map/CityMapView.kt`) — free, no API key or account needed, works out of
+the box. (An earlier iteration tried the native 2GIS MapKit SDK instead;
+dropped because getting a working mobile-SDK key from 2GIS turned out to be
+a sales-mediated B2B process, not a quick self-serve signup — see git
+history if that's ever worth revisiting.)
 
 ## Notes / current scope
 
 This is iteration 1: Moscow only (Gorky Park, Red Square area, Moscow-City),
 no user accounts (favorites are local/Room-only), no speed/heading-aware
 auto content-length selection yet (reserved API params exist, unused).
-Nearby-search radius caps at 10km. Place markers aren't yet plotted on the
-real 2GIS map (only the placeholder does that) — follow-up work.
-
-The 2GIS REST/JS API key above is used directly via
-`local.properties`/`BuildConfig` for development convenience — don't ship it
-as-is in a public repo. Same goes for `dgissdk.key` once you have one.
+Nearby-search radius caps at 10km.