merge: reconcile master particle-wind work with origin/main redesign

Merged divergent branches (common ancestor a9d87b6). Took origin/main
as base (layer manager, recenter, quit button, GPX tracks, marine
conditions, dark theme, user position layer, active/past track layers)
and layered in particle wind simulation work:

- MapHandler: added setupWindLayer, updateWindLayer, updateWindGridLayer;
  kept their user-pos layer, follow/recenter state, active+past tracks
- WeatherRepository: kept their fetchCurrentConditions, added fetchWindGrid
- MainViewModel: kept their track/marine/summary changes, added windGrid
  StateFlow, loadWindGrid, buildGrid
- MainActivity: kept their full UI (layer picker, quit, recenter, fade
  animations), added particleWindView wiring, weatherLoaded guard,
  windArrow/windGrid observers
- activity_main.xml: took their LinearLayout redesign, added ParticleWindView
  overlay inside ConstraintLayout

https://claude.ai/code/session_01HXPjBsogsJVRwCiekDGkJX

1 files changed, 59 insertions, 0 deletions

diff --git a/docs/superpowers/specs/2026-04-03-map-interaction-design.md b/docs/superpowers/specs/2026-04-03-map-interaction-design.md
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+# Map Interaction Design
+_2026-04-03_
+
+## Overview
+
+Enable free map pan/zoom while keeping GPS auto-follow as the default. When the user gestures on the map, the UI hides and a Recenter button appears. Tapping Recenter restores auto-follow and the full UI.
+
+## State
+
+A single `isFollowing: Boolean` flag owned by `MapHandler`. Starts `true`. This is the only piece of new state.
+
+## Entering Manual Mode
+
+`MapLibreMap.addOnCameraMoveStartedListener` fires with `REASON_API_GESTURE` when the user initiates a pan, pinch-zoom, or rotate. On that event:
+
+- `MapHandler.isFollowing` → `false`
+- `MapHandler` emits via a new `StateFlow<Boolean> isFollowing` exposed to MainActivity
+- `MapHandler.centerOnLocation()` becomes a no-op while `!isFollowing` — GPS updates still arrive, last position is stored
+
+## Returning to Auto-Follow
+
+`fab_recenter` click handler:
+
+- Calls `MapHandler.recenter()` — sets `isFollowing = true`, calls `centerOnLocation(lastLat, lastLon)`
+- `isFollowing` StateFlow emits `true` → MainActivity restores UI
+
+## UI Changes
+
+### New element: `fab_recenter`
+
+- Pill-shaped button (`wrap_content` width, 40dp height, 20dp corner radius)
+- Label: "⊙ Recenter"
+- Position: centered horizontally, `24dp` above the bottom of the map `ConstraintLayout`
+- `android:visibility="gone"` by default
+- Elevation: 20dp (above the instrument sheet)
+
+### Visibility toggling (MainActivity)
+
+When `isFollowing` → `false`:
+- Fade out (alpha 0, 150ms): `instrument_bottom_sheet`, `bottom_navigation`, `fab_mob`, `fab_record_track`
+- Show `fab_recenter` (visibility VISIBLE, fade in 150ms)
+
+When `isFollowing` → `true`:
+- Hide `fab_recenter` (fade out 150ms, then GONE)
+- Fade in (alpha 1, 150ms): `instrument_bottom_sheet`, `bottom_navigation`, `fab_mob`, `fab_record_track`
+
+## Files to Change
+
+| File | Change |
+|------|--------|
+| `MapHandler.kt` | Add `isFollowing` StateFlow, `lastLat`/`lastLon` storage, `recenter()`, guard in `centerOnLocation()`, register `OnCameraMoveStartedListener` |
+| `activity_main.xml` | Add `fab_recenter` pill button |
+| `MainActivity.kt` | Observe `mapHandler.isFollowing`, animate UI in/out, wire `fab_recenter` click |
+
+## Out of Scope
+
+- Tapping the map (without gesture) to restore UI — not requested
+- Timeout to auto-restore UI — not requested
+- Zoom-level persistence across recenter — not requested