Add a dayTintProvider plugin hook

Lets a plugin colour-code days in the Plan sidebar. trip-segments can
already announce "Kanazawa begins" in the day plan, but it can't make
day 12 look like it belongs to Kanazawa.

dayScheduleProvider can't cover this: it renders a fixed row, and it's
capped at 60 items per provider, so one item per day would tint the
first 60 days of a six-month trip and silently stop. This hook is
bounded by day count instead.

GET /api/day-tints/:tripId returns per-day tones for three regions of a
day card - the number badge (also the mobile day chip), the header row,
and the expanded activity list. `tone` is a shorthand filling every
region a contribution doesn't name; unnamed regions render as they do
today. Tones only, never hex, so the host can pick the alpha per theme
and per region.

One contribution per day, resolved whole: first entry wins within a
provider, first granted provider wins across plugins.

wiki/Plugin-Development.md

@@ -668,6 +668,7 @@ module.exports = definePlugin({
 | `mapLayerProvider.getLayers(tripId, ctx)` → `MapLayerContribution[]` | `hook:map-layer-provider` | **live** — bounded vector overlays on the trip map: a computed route, a reachable-range corridor, a zone. Each layer is `{id, name?, features}` with features `{type: 'polyline'\|'polygon'\|'circle', points?/center?+radiusM?, tone?, width?, dash?, opacity?, fill?, label?}`. Styling stays in the tone palette; width (1–8), opacity (0.05–1) and radius (≤2000 km) are clamped, `dash` is an enum. Budgets per plugin: ≤4 layers, ≤150 features, ≤8000 vertices, ≤2000 vertices/shape — an oversized or partly-invalid shape is dropped whole, never truncated. Declarative only; drawn beneath TREK's own day route on both the Leaflet and GL renderers. Also `GET /api/map-layers/:tripId` |
 | `routeProvider.getRoute(request, ctx)` → `RouteProviderResult` | `hook:route-provider` | **live** — routes a day's stops under one of the plugin's declared `capabilities.routeProfiles` (an EV profile with charging stops, a scenic profile…). `request` is `{tripId, dayId, profile, waypoints}` (2–30 located stops in visit order); the result is `{coordinates, distance, duration, legs, viaPoints?}` and is validated **whole**: ≤10000 vertices, `legs` must be exactly `waypoints−1` entries (each `{distance, duration, note?}` — `note` ≤120 chars shows on the sidebar connector), ≤40 via points (`{lat, lng, label?, tone?, dwellSeconds?}` drawn as stops on the route line). A malformed result is discarded and the planner falls back to straight lines. **Targeted, not a fan-out**: TREK calls exactly the provider whose profile the user picked in the route toggle, with a 20 s timeout (room to call an external solver through your declared egress). `POST /api/plugin-routes/:pluginId/:profileId` |
 | `dayScheduleProvider.getSchedule(tripId, ctx)` → `DayScheduleContribution[]` | `hook:day-schedule-provider` | **live** — time contributions rendered into the day plan on desktop and mobile: "35 min charging at this stop", "45 min security before this flight". Each is `{id, dayId, assignmentId?/reservationId?/position?, minutes?, label, tone?}` — anchored under a place/booking row or at a day's start/end (default end). `dayId` must belong to the trip (checked server-side), `minutes` (1–1440) is shown on the row **and folded into the day's route-footer total**, `label` ≤120 chars, ≤60 items/plugin. Also `GET /api/day-schedule/:tripId` |
+| `dayTintProvider.getDayTints(tripId, ctx)` → `DayTintContribution[]` | `hook:day-tint-provider` | **live** — colours painted into a day card in the Plan sidebar (and into that day's mobile chip), so a trip split into legs shows its leg membership while you scroll. Each is `{dayId, tone?, badgeTone?, headerTone?, activityTone?, label?}`. The card has **three separately tintable regions** — the day-number badge (also the mobile chip), the header row, and the expanded activity list — so a plugin can mark the leg boldly on the badge while leaving the dense activity list plain; `tone` is the shorthand that fills every region you do not name, and an unnamed region renders exactly as it does with no plugin. Tone only, never a hex: the host picks the alpha per theme **and** per region, so the tint stays subtle in light and dark and a tinted header hovers to a deeper mix of its own tone. `dayId` must belong to the trip (checked server-side), `label` ≤ 60 chars becomes the day's tooltip, raw array sliced at 2000. **A day takes at most one contribution, resolved whole**: within your own list the first entry for a day wins, and across plugins the first granted provider wins — so a day never flickers between colours, and a losing plugin cannot fill in the winner's untinted regions. Bounded by the trip's day count rather than a fixed item cap, which is why this is not `dayScheduleProvider` (≤60 items would tint only the first 60 days of a long trip). Also `GET /api/day-tints/:tripId` |
 | `pdfSectionProvider.getSections(tripId, ctx)` → `PdfSection[]` | `hook:pdf-section-provider` | **live** — text-only sections appended to the trip PDF export. Each is `{title, paragraphs?, table?}`; the host escapes and lays everything out itself (no markup ever reaches the document), caps counts (≤5 sections/plugin, ≤20 paragraphs, ≤8 headers, ≤50 rows) + lengths (title 120, paragraph 2000, header 60, cell 200) and clips rows to the header width. Also `GET /api/pdf-sections/:tripId` |
 | `atlasLayerProvider.getLayers(ctx)` → `AtlasLayer[]` | `hook:atlas-layer-provider` | **live** — country tint layers drawn over the Atlas world map (wishlists, advisories, …). **User-scoped**: the host binds the acting user, the hook takes no target parameter. Each layer is `{id, name?, countries: [{code, tone?, label?}]}`; codes must be ISO-3166 alpha-2 (uppercase-coerced), tone is enum-whitelisted, counts capped (≤3 layers/plugin, ≤300 countries/layer). Declarative only — plugin JS never runs on the map canvas. Also `GET /api/atlas-layers` |
 | `journalEntryProvider.getRows(entryId, ctx)` → `{ label, value?, url? }[]` | `hook:journal-entry-provider` | **live** — extra rows rendered under a journal entry card (needs the Journey addon; the entry's journey is access-checked like the journal detail routes). Same hardening as place details plus server-side normalization: ≤12 rows/plugin, label ≤60, value ≤200, url http/https/mailto-only. Also `GET /api/journal-entry-rows/:entryId` |
@@ -1185,6 +1186,7 @@ guard optional `ctx.*` namespaces.
 | `hook:map-layer-provider` | `hooks.mapLayerProvider` — bounded vector overlays (routes, corridors, zones) on the trip map |
 | `hook:route-provider` | `hooks.routeProvider` — routing profiles for the planner's route toggle (declared in `capabilities.routeProfiles`) |
 | `hook:day-schedule-provider` | `hooks.dayScheduleProvider` — time contributions in the day plan (charging, buffers), totalled in the route footer |
+| `hook:day-tint-provider` | `hooks.dayTintProvider` — colours for a day card's badge / header / activity list in the Plan sidebar (e.g. which leg of the trip a day belongs to). One contribution per day: first granted provider wins |
 | `hook:pdf-section-provider` | `hooks.pdfSectionProvider` — sections appended to the trip PDF export |
 | `hook:atlas-layer-provider` | `hooks.atlasLayerProvider` — per-user country tint layers on the Atlas map |
 | `hook:journal-entry-provider` | `hooks.journalEntryProvider` — extra rows on a journal entry card |