Reservation end time, route perf overhaul, assignment search fix

- Add reservation_end_time field (DB migration, API, UI)
- Split reservation form: separate date, start time, end time, status fields
- Fix DateTimePicker forcing 00:00 when no time selected
- Show end time across all reservation displays
- Link-to-assignment and date on same row (50/50 layout)
- Assignment search now shows day headers for filtered results
- Auto-fill date when selecting a day assignment
- Route segments: single OSRM request instead of N separate calls (~6s → ~1s)
- Route labels visible from zoom level 12 (was 16)
- Fix stale route labels after place deletion (useEffect triggers recalc)
- AbortController cancels outdated route calculations

server/src/db/database.js

@@ -182,6 +182,7 @@ function initDb() {
       assignment_id INTEGER REFERENCES day_assignments(id) ON DELETE SET NULL,
       title TEXT NOT NULL,
       reservation_time TEXT,
+      reservation_end_time TEXT,
       location TEXT,
       confirmation_number TEXT,
       notes TEXT,
@@ -606,6 +607,10 @@ function initDb() {
       try { _db.exec('ALTER TABLE trip_files ADD COLUMN note_id INTEGER REFERENCES collab_notes(id) ON DELETE SET NULL'); } catch {}
       try { _db.exec('ALTER TABLE collab_notes ADD COLUMN website TEXT'); } catch {}
     },
+    // 28: Add end_time to reservations
+    () => {
+      try { _db.exec('ALTER TABLE reservations ADD COLUMN reservation_end_time TEXT'); } catch {}
+    },
     // Future migrations go here (append only, never reorder)
   ];