Filters apply live everywhere, and every route calendar honours the trip-span cap

[davd-gzl]

Follow-up to #64, closing the two gaps that fix left open.

1. A filter now applies live — the results follow it, not just the form calendar

#64 made the form calendar repaint on a filter change, but the results — the list and the possible-days / return calendars inside it — kept grading the old budget until Search was pressed again. Changing "Max correspondances" while looking at a route left the page half-updated.

A filter is one deliberate choice, not a half-typed field, so applyFilterChange now repaints the form calendar and refreshes the results for that route in place: same history entry, applied value in the URL. Wired to every filter plus the radius, the trip span, hidden trains and the Ideas/tour region.

The staged-edit model is untouched where it earns its keep:

• a typed route (departure, destination, legs, cities) still waits for Search — the search must not chase keystrokes;
• a filter change never smuggles a staged route in: the refresh is skipped whenever the form's route, legs, cities or date no longer match what is on screen;
• the bare landing form and the post-reload "press Search" prompt stay staged — nothing on screen to bring up to date, and a search must not start behind that prompt.

2. Every exact-route calendar honours "max trip span (days)"

The Advanced span cap applied to the journey lists only, so a calendar could show a green day whose list the cap then emptied — a dead-end day. odJourneyOptsFor now returns the widened day pool and the accept-filter together, and the one-way calendar, the round-trip return calendar and the form calendar all grade with it: the same sweep their list runs. It also collapses the three duplicated passesVia + withinSpan filter pairs into one accept.

Verification

• Real browser, built app + committed snapshot: Paris → Toulouse, raising the filter refreshes the page live (0 → 8 green days, 69 journeys, conn=2 in the URL, no new history entry); with 3 changes the results calendar drops from 8 green days to 6 under a 1-day span, matching the trains actually listed.
• Tests: staged route edit vs live filter change (and that a filter can't commit a staged route), the reload prompt still owning the first run, and odJourneyOptsFor's span cap + via hub — 156 unit tests, plus a new E2E scenario for the live filter (15/15).
• Gates: tsc --noEmit, npm test, npm run build, npm run test:e2e.

docs/user-flows.md updated with the live-filter/staged-route contract and the span-aware calendars (and two stale builder names in the calendar table corrected).

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