feat(tours): a hike can be marked as a winter hike or a snowshoe hike

HIK-01. The details of the hiking planner gain an optional Winter activity
switch, off by default, so the normal hiking flow asks for nothing more.
Switched on, the hike is a winter hike or a snowshoe hike; the choice stays
dimmed and out of reach while the switch is off. The label is saved with the
tour, comes back when it is opened, survives a draft reload, a copy and a
take-over, and switching it off takes only the label away: the route, its
grade and the days stay as they were.

The label is a label only. Routing, the walking time and the 3D terrain view
work as for any hike, and the info dot and the head pill's tooltip say that
nothing was checked for snow, avalanches or whether a path can be walked in
winter. The saved label shows as a frosted snowflake on the corner of the
tour's tile in the tour list and the day plan, and as a pill beside the type
in the tour's detail.

The server keeps it in tours.winter_activity (CHECK list, NULL for every tour
saved before and for every other type), refuses it on a bike tour, a city walk
and a paddle tour, and keeps the stored label when an older client saves a
hike without the field. A snowshoe hike exports to GPX as snowshoeing.
list_tours names the field, with the same words on what it does not say.

wiki/MCP-Addon-Tools.md

@@ -237,7 +237,7 @@ The saved tours of a trip, as the Tours list and the tour detail show them, how
 
 | Tool | Description | Scope |
 |---|---|---|
-| `list_tours` | The saved tours of a trip: name, type (`hike`, `walk` for a city walk, `bike`, or `kayak` for a paddle tour), origin (`trek` for planned in TREK, `gpx` for a GPX import, `wanderer` for a wanderer snapshot), distance, ascent and descent (unknown for a paddle tour drawn in the planner), the stored routing limit of a hike on the SAC scale and its route choices (`hiking_preferences`), the boat, water and chosen speed of a paddle tour, the check bench of a paddle tour (`paddle_check`: how far the OpenStreetMap obstacle data covers its route and how many obstacles are open, to check again or decided; a planning status, never a safety or legal clearance), for a city walk how many stations it has (`station_count`), their stays as far as entered and how many have none, whether a tour still waits for its way to be planned (`route_pending`: saved with its points only, its distance and walking time unknown until someone opens it in the planner and saves it), the `revision` (raised by every saved change of the tour), and the days of the trip each tour is on | `trips:read` |
+| `list_tours` | The saved tours of a trip: name, type (`hike`, `walk` for a city walk, `bike`, or `kayak` for a paddle tour), origin (`trek` for planned in TREK, `gpx` for a GPX import, `wanderer` for a wanderer snapshot), distance, ascent and descent (unknown for a paddle tour drawn in the planner), the stored routing limit of a hike on the SAC scale and its route choices (`hiking_preferences`), the winter label of a hike (`winter_activity`: `winter_hike` or `snowshoe`; a label only, the route and its time are planned as for any hike, never a statement about winter conditions), the boat, water and chosen speed of a paddle tour, the check bench of a paddle tour (`paddle_check`: how far the OpenStreetMap obstacle data covers its route and how many obstacles are open, to check again or decided; a planning status, never a safety or legal clearance), for a city walk how many stations it has (`station_count`), their stays as far as entered and how many have none, whether a tour still waits for its way to be planned (`route_pending`: saved with its points only, its distance and walking time unknown until someone opens it in the planner and saves it), the `revision` (raised by every saved change of the tour), and the days of the trip each tour is on | `trips:read` |
 | `get_tour_plan` | One tour: its facts, its ordered control points, its provenance (where it came from, when, and whether it was changed in TREK since) and its days. A control point can carry a fixed leg to the next one: a via ferrata (`ferrata`) or a stretch drawn by hand (`free`), which no router planned or checked. A shaping point (`shaping: true`) only steers the route and is no stop. A paddle tour also carries its obstacle checklist (`obstacle_check`): the obstacles of the OpenStreetMap data along its route, what the travellers decided about each, and their own portages and locks. The stations of a city walk carry every field spelled out: `key` (the same across saves), `name`, `stay_minutes` (`0` for a point only passed, `null` when not known), `importance` (`optional`, `must`, or `null` for normal), `protected` (a station a proposed change has to keep where it is; the travellers can still edit it) and `opening_hours` (as OpenStreetMap writes them, `null` when none is known). The full track geometry is not included | `trips:read` |
 | `find_tours_for_day` | The tours put on one day of a trip, with the same facts as `list_tours` | `trips:read` |
 | `get_city_walk_progress` | How far a city walk got on one day it is on: every station in order with its key, its status that day (planned, visited or skipped, as checked off in the day plan), importance, protection, stay and opening hours, what is still open, and the walking time of the whole walk. Visits belong to that day only. Reading changes nothing | `trips:read` |