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/V3-05-mounted-mode.md

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+# V3-05 — Mounted (handlebar) mode
+
+**Phase** Live map · **Depends on** V3-04 · **Size** M · **Status** Not started
+
+## Goal
+Make the app usable on handlebars in daylight, at speed, with gloves — as an explicit mode
+rather than an accident.
+
+## Context
+v1 and v2 were built entirely around "start it, pocket it, stop it". **A mounted phone is a
+different product.** Treating it as a mode makes the differences deliberate instead of
+half-met.
+
+## Design
+A toggle that changes several things at once:
+
+- **Keep the screen awake** for the whole ride (`wakelock_plus`). Currently the screen
+  sleeps and recording continues; mounted, that is wrong.
+- **Sunlight legibility.** The dark theme was chosen for glanceability at night and in a
+  pocket-glance. Behind a visor in daylight it is the wrong choice — a high-contrast
+  variant with larger figures is needed. This is not the same as V3-16's visual identity.
+- **Larger touch targets still.** 72 dp works stopped; at speed with gloves it does not.
+- **Interruptions.** What happens on an incoming call or a notification — the recording
+  must survive and the screen must come back.
+
+## Implementation
+1. `mountedMode` in `Config`, surfaced in settings and as a quick toggle on the record
+   screen
+2. `wakelock_plus`, acquired on start when mounted, released on stop/pause — and released
+   on `dispose`, or the screen stays lit after the app closes
+3. A high-contrast text scale applied when mounted
+4. Handle `AppLifecycleState.inactive` (a call arriving) distinctly from `paused`
+
+## Acceptance criteria
+- [ ] Mounted: the screen never sleeps during a ride
+- [ ] Un-mounted: behaviour is exactly as today
+- [ ] The wake lock is released on stop, on discard, and on app exit
+- [ ] An incoming call does not stop recording
+- [ ] Battery cost of mounted mode is measured and written down (V3-13)
+
+## Tests
+- Widget: mounted toggle changes text scale and requests the wake lock (fake the plugin)
+- Widget: the lock is released on stop
+- **Manual, on a real bike** — legibility in daylight cannot be tested any other way
+
+## Risks
+- **A leaked wake lock flattens the battery**, silently and after the app is closed. Test
+  the release path harder than the acquire path.
+- Legibility is a judgement call that needs a real ride in real sun.
+
+## Out of scope
+A dedicated mounted layout with different information architecture — start by scaling what
+exists and see what the ride teaches.