Break v3 into 16 tickets

One file per feature, in the v2 shape that worked: goal, context, design,
implementation, acceptance criteria, tests, risks, out of scope -- written before
implementing so the risks are on paper rather than walked into.

Three carry more weight than their size suggests. V3-01 ships the port's first
real migration, and since the destructive fallback is gone, getting addColumn and
a v1-database test right matters more than the feature. V3-08 forces a
routing-engine decision with ongoing cost, so it sits behind a RoutingService
interface mirroring what LocationSource did for GPS. V3-13 is not code at all --
it answers the three questions open since v2, and V3-15 may close unbuilt as a
result, which is a legitimate outcome.

Several tickets record constraints that are easy to lose: no activity picker in
front of Start, because the founding premise is press-and-go with gloves; the
Route-to-Trip foreign key must not cascade, or deleting an old plan deletes the
ride; V3-14 will deliberately break the parity harness by adding GPX <type>, and
that expectation should be updated rather than the check dropped; and V3-16 must
not regress the explicit text colours that exist because of the black-on-black bug.

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

docs/v3/V3-04-live-map.md

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+# V3-04 — Live map on the recording screen
+
+**Phase** Live map · **Depends on** nothing · **Size** M · **Status** Not started
+
+## Goal
+While recording, show the path as it is drawn, on the recording screen.
+
+## Context
+v2 shipped without one deliberately: the phone rides in a pocket, so a live map would burn
+battery for something nobody is looking at. **That decision is reversed** — Dylan wants it
+for visual appeal, and because a mounted phone is now a real use case (V3-05).
+
+The map component already exists (`RideMap`) and already handles per-segment polylines,
+render-only decimation and the zoom clamp. This ticket is mostly about *lifecycle*, not
+drawing.
+
+## Design
+Two constraints survive the reversal and are non-negotiable:
+
+- **`RecordingEngine` must never reference a map.** Rendering belongs to a visible screen's
+  widget lifecycle. The engine already exposes everything needed.
+- **No tile fetch or redraw while backgrounded.** A pocketed phone must cost exactly what
+  it costs today.
+
+Feed the map from a stream of the current trip's points. `watchTripStats` exists but
+returns aggregates; this needs the points themselves — add a `watchPointsForTrip` Drift
+stream, which updates naturally on each writer flush (~2 s), not per fix.
+
+Follow the rider: keep the latest point centred, with a manual-pan override that stops
+auto-follow until re-enabled.
+
+Behind the existing map toggle, off by default while it is unproven on battery.
+
+## Implementation
+1. `watchPointsForTrip(tripId)` in `AppDatabase`
+2. Hoist the map above the stats card on the record screen, behind the toggle
+3. `WidgetsBindingObserver` — on `AppLifecycleState.paused`, stop tile fetching; resume on
+   `resumed`. This is the load-bearing part.
+4. Auto-follow with a pan override
+5. Keep the numeric readout visible; the map must not push SPEED off screen (the record
+   screen already scrolls — see the overflow fix in `port/PROGRESS.md`)
+
+## Acceptance criteria
+- [ ] The path appears and extends while recording
+- [ ] Backgrounding the app stops all tile activity, verified in a network log
+- [ ] `RecordingEngine` still has no map import — grep it
+- [ ] With the toggle off, no map widget is constructed at all
+- [ ] Speed and elapsed remain visible without scrolling on a common phone size
+
+## Tests
+- Widget: map appears only when recording and the toggle is on
+- Widget: lifecycle transition to paused stops the tile layer
+- The existing map tests still pass
+
+## Risks
+- **Battery.** This is the whole reason v2 said no. Measure before defaulting it on
+  (V3-13).
+- Redrawing per fix rather than per flush would be wasteful; drive from the database
+  stream, which is already batched.
+
+## Out of scope
+Mounted mode (V3-05). Other riders on the map (v4).