feat(schedule_type): minute-precision windows + variable maintenance length

Lifts the two hard restrictions in PR #18:
  * window bounds were `int hour` (0-23) → now `int minutes-since-UTC-midnight` (0-1439)
  * maintenance window was exactly 1 hour → now any duration in [1, 180] minutes
    ((maint_to - maint_from) mod 1440)

## Schema migration (additive)

`_migrate_schema()` detects legacy "hours" rows (any row where MAX of the
6 window columns is ≤ 23) and multiplies each column by 60 to convert
to minutes. Idempotent — post-conversion values are well above 23 so
the guard never fires twice.

## Touched surfaces

- `models/schedule_type.py` — column comments updated; new
  `compute_maintenance_duration()` helper (returns 1-1440 min, treats
  from==to as 1440 which is then rejected by validator)
- `schemas/schedule_type.py` — `*_from`/`*_to` upper bound 23 → 1440;
  `_validate_maintenance_window` accepts 1-180min duration; response
  includes derived `maintenance_duration_minutes`
- `schemas/schedule_type_special_slot.py` — `minute_in_window` max
  59→179; `estimated_duration` max 60→180
- `routers/schedule_type.py` — PATCH re-validates merged maintenance
  pair (partial updates can put the row into an invalid combo the
  pydantic single-field validator can't catch); `_attach_derived`
  populates the new response field
- `routers/schedule_type_special_slot.py` — `_validate_fits_window`
  now takes the parent's maintenance duration instead of hard-coded 60
- `routers/calendar.py` — `_scheduled_inside_window` arg renamed
  hour→min; the maintenance-window guard error message formats
  HH:MM not HH:00
- `services/special_slot_materialiser.py` — materialised
  `scheduled_at` derived from `(maint_from_min + tpl.minute_in_window)`
  with hour/minute split

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/main.py

@@ -400,9 +400,9 @@ def _migrate_schema():
             db.execute(text("ALTER TABLE agents ADD COLUMN schedule_type_id INTEGER NULL"))
 
         # --- schedule_types: add maintenance_from / maintenance_to ---
-        # Default 8:00–9:00 UTC for existing rows; the 1-hour-window
-        # invariant is enforced at the schema level for any NEW rows by
-        # the pydantic ScheduleTypeCreate validator.
+        # Default 8:00–9:00 UTC for existing rows; the maintenance
+        # duration invariant (1-180min) is enforced at the schema
+        # level for any NEW rows by ScheduleTypeCreate validator.
         if _has_table(db, "schedule_types"):
             if not _has_column(db, "schedule_types", "maintenance_from"):
                 db.execute(text(
@@ -413,6 +413,29 @@ def _migrate_schema():
                     "ALTER TABLE schedule_types ADD COLUMN maintenance_to INT NOT NULL DEFAULT 9"
                 ))
 
+            # --- minutes-since-midnight migration (PR #21+) ---
+            # The 6 schedule_type window columns used to hold *hours*
+            # (0-23). PR #21 changed semantics to *minutes since UTC
+            # midnight* (0-1439). Detect the legacy regime by checking
+            # if ANY row has all 6 values ≤ 23 — if so, multiply each
+            # by 60 to convert. Idempotent: post-conversion values are
+            # all ≥ 0 and usually well above 23, so guard never fires
+            # twice.
+            row = db.execute(text(
+                "SELECT MAX(GREATEST(work_from, work_to, entertainment_from, entertainment_to, maintenance_from, maintenance_to)) AS m "
+                "FROM schedule_types"
+            )).fetchone()
+            if row is not None and row.m is not None and row.m <= 23:
+                db.execute(text(
+                    "UPDATE schedule_types SET "
+                    "  work_from = work_from * 60, "
+                    "  work_to = work_to * 60, "
+                    "  entertainment_from = entertainment_from * 60, "
+                    "  entertainment_to = entertainment_to * 60, "
+                    "  maintenance_from = maintenance_from * 60, "
+                    "  maintenance_to = maintenance_to * 60"
+                ))
+
         # --- time_slots: admin-locked + special_slot pointer ---
         if _has_table(db, "time_slots"):
             if not _has_column(db, "time_slots", "is_admin_locked"):