Cleanup: small-exhaust sweep from the 2026-07-16 debt review

[bmander]

Mechanical, behavior-neutral cleanup of the "exhaust" left by the map-focus sprint (#1865/#1892/#1893) and the dependency-bump wave. This is the batch of small quick-wins from the 2026-07-16 debt review; the substantive findings are filed separately as #1901–#1912.

No functional change. Verified: obaGoogle + obaMaplibre Kotlin compile clean under -PwarningsAsErrors=true, and FocusedTripRepositoryTest passes.

Docs / comment drift

• CLAUDE.md: Kotlin version parenthetical 2.3.20 → 2.4.10.
• libs.versions.toml: drop the stale "kotlin-stdlib-jdk7 pins to this" clause; correct the KSP comment — KSP2 is versioned independently of Kotlin (plain semver), not the old kotlinVersion-kspVersion format.
• build.gradle.kts: drop the DataStore "1.0.0 was the minSdk-21 pin / adopt a newer one as a follow-up" comment — that bump (to 1.2.1) already landed.
• Remove orphaned "trip-stop dots" references in both renderers' class docs and the clearStatic() / info-window comments (TripStopBitmaps.kt was deleted in Add adjacency-aware stop and route focus to the map #1865; stops are now reconciled in place).
• MaterialSymbols: document the Symbols source axes (24dp / weight 400 / grade 0 / outlined) so the hand-transcribed paths can be regenerated or verified, and steer new icons toward baseline_*_24.xml drawables.
• MapRenderState: point the two MapLibre route-badge deferral comments at the new tracking issue MapLibre: implement the adjacency route-badge layer (parity with Google, #1827) #1913.

Dead code / dedup

• Delete the test-only FocusedTripStops.stopIds convenience property (production code uses stopIdsByTripId directly); inline the flatten into its two test assertions.
• Hoist the duplicated Web-Mercator constant (156543.033…) into a single shared METERS_PER_PIXEL_AT_EQUATOR_ZOOM_ZERO in map/render/GeoMath.kt. GoogleMapRenderer now uses it instead of an inlined, less-precise literal (156543.03392).

Frozen dependencies

• Remove firebase-core 21.1.1 — a discontinued empty umbrella artifact; firebase-analytics is already a direct dependency.
• Remove kotlin-stdlib-jdk7 — merged into kotlin-stdlib since Kotlin 1.8; the Kotlin Gradle plugin adds the stdlib automatically.

Deliberately left out of this PR

These appeared in the review's "small exhaust" list but are secretly medium-effort or behavior-touching, so they stay as their own follow-ups rather than riding in a mechanical cleanup:

• CurrentFocusPersistence parallel-arrays → @Parcelize (serialization change; its legacy-migration branch has no test).
• The copy-pasted async fetch blocks in RouteMapController.focusStop (folds naturally into the controller refactor, RouteMapController: make presentation assembly pure and testable (1,024-line controller; focus-session machine untested) #1907).
• RouteBadgeLayout.MeasuredPath ↔ util/Polyline arc-length merge (needs a GeoPoint-based Polyline).
• start()'s 5-param mirror of ShowRouteRequest (behavior-touching; tracked at MapViewModel.toRoute()'s two branches can silently diverge on which ShowRouteRequest fields they honor #1797).
• Moving BoundedLruCache from extrapolation/data/ to util/ (cross-package import churn for low value).

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