Add locations (Filialen) as a grouping layer above resources

Enables multiple barbers/staff bookable at the same location and time
-- previously "resource" conflated "location" and "the thing that
can't double-book itself" into one row, so a Filiale could only ever
have exactly one bookable slot at once.

- New `locations` table; `resources.location_id` with a generic,
  idempotent backfill migration (any resource without a location gets
  one auto-created matching its name -- not a one-off for any single
  client, protects any future resource stuck in the old flat shape too)
- `resources`/`resource_hours`/services keep everything they already
  had (hours, min-notice, max-advance, buffer, the no-overlap
  constraint) scoped to resource_id, not location_id -- two barbers at
  one location must stay independently bookable at the same time
- booking_db.py: new locations CRUD mirroring the existing
  resources/services pattern; create_resource now requires a
  location_id, guarded the same way every other tenant check here is
  (get_location existence check, no real FK -- matches this schema's
  existing no-FK convention throughout)
- app.py: new POST /api/locations provisioning route; POST
  /api/resources now requires location_id
- owner_settings.py + settings.html: new self-service "add a Filiale"
  / "add a barber" UI -- there was previously no way to create a
  resource at all outside the CRM/n8n provisioning API
- public_booking.py + book.html: new Filiale picker (reuses the
  existing wireOptionGroup button-group pattern), filtering the
  Mitarbeiter picker to the selected location -- a single-location
  client sees no extra click, same as before Filialen existed
- owner_booking.py + agenda.html: the Filiale show/hide toggle and
  hide-cancelled toggle (shipped earlier this session) now key off
  location_id instead of resource_id, so hiding a Filiale hides every
  barber's bookings at it; manual-booking dropdown grouped by Filiale
- n8n/onboarding.json: default provisioning now creates a "Hauptfiliale"
  location before its resource (inert until re-imported into the live
  n8n instance)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backoffice/db/init.sql

@@ -101,6 +101,25 @@ CREATE TABLE IF NOT EXISTS credentials (
 -- Booking module (#15): resources, services, and the users / password-reset
 -- tables the owner-login tickets build on. All access goes through
 -- app/booking_db.py — see that module for the tenancy-safe data-access layer.
+--
+-- Locations (Filialen) group resources for display/selection purposes only --
+-- the actual bookable/concurrency-safe unit stays `resources` (a client with
+-- several staff at one location needs each staff member independently
+-- bookable at the same time, so hours/notice/buffer/the no-overlap
+-- constraint all stay keyed on resource_id, not location_id). No FK to
+-- clients or from resources.location_id to here, matching this whole
+-- schema's convention: no real FKs anywhere, tenant/existence integrity is
+-- enforced in app/booking_db.py via get_location()/get_resource()-style
+-- checks before every write.
+CREATE TABLE IF NOT EXISTS locations (
+    location_id  text PRIMARY KEY,
+    client_id    text NOT NULL,
+    name         text NOT NULL,
+    active       boolean NOT NULL DEFAULT true,
+    created_at   timestamptz NOT NULL DEFAULT now(),
+    updated_at   timestamptz NOT NULL DEFAULT now()
+);
+
 CREATE TABLE IF NOT EXISTS resources (
     resource_id         text PRIMARY KEY,
     client_id           text NOT NULL,
@@ -190,6 +209,25 @@ ALTER TABLE clients ADD COLUMN IF NOT EXISTS timezone     text NOT NULL DEFAULT
 ALTER TABLE clients ADD COLUMN IF NOT EXISTS auto_confirm boolean NOT NULL DEFAULT true;
 ALTER TABLE clients ADD COLUMN IF NOT EXISTS ics_token    text;
 
+ALTER TABLE resources ADD COLUMN IF NOT EXISTS location_id text;
+
+-- Generic, permanent backfill (not a one-off for any single client): any
+-- resource stuck in the old flat shape (location_id IS NULL) gets a brand
+-- new location auto-created with its own name and is attached to it. Keeps
+-- protecting against a future resource ending up without a location -- a
+-- provisioning bug, a manual INSERT, a restored backup -- since a resource
+-- with location_id already set is never touched again by this block.
+DO $$
+DECLARE r RECORD; new_loc_id text;
+BEGIN
+  FOR r IN SELECT resource_id, client_id, name FROM resources WHERE location_id IS NULL LOOP
+    new_loc_id := 'LOC-' || floor(extract(epoch FROM clock_timestamp()) * 1000)::bigint
+                   || '-' || substr(md5(random()::text), 1, 6);
+    INSERT INTO locations (location_id, client_id, name) VALUES (new_loc_id, r.client_id, r.name);
+    UPDATE resources SET location_id = new_loc_id WHERE resource_id = r.resource_id;
+  END LOOP;
+END $$;
+
 -- keep updated_at fresh on row changes
 CREATE OR REPLACE FUNCTION touch_updated_at() RETURNS trigger AS $$
 BEGIN NEW.updated_at = now(); RETURN NEW; END;
@@ -204,7 +242,7 @@ DO $$
 DECLARE t text;
 BEGIN
   FOREACH t IN ARRAY ARRAY['clients','leads','projects','bookings','invoices',
-                           'credentials','resources','services','users'] LOOP
+                           'credentials','locations','resources','services','users'] LOOP
     EXECUTE format(
       'CREATE OR REPLACE TRIGGER %I_touch BEFORE UPDATE ON %I FOR EACH ROW EXECUTE FUNCTION touch_updated_at()',
       t, t);
@@ -215,7 +253,9 @@ CREATE INDEX IF NOT EXISTS leads_received_idx   ON leads (received_at DESC);
 CREATE INDEX IF NOT EXISTS clients_status_idx   ON clients (status);
 CREATE INDEX IF NOT EXISTS activity_ts_idx      ON activity_log (ts DESC);
 CREATE INDEX IF NOT EXISTS credentials_client_idx ON credentials (client_id);
+CREATE INDEX IF NOT EXISTS locations_client_idx ON locations (client_id);
 CREATE INDEX IF NOT EXISTS resources_client_idx ON resources (client_id);
+CREATE INDEX IF NOT EXISTS resources_location_idx ON resources (location_id);
 CREATE INDEX IF NOT EXISTS services_client_idx  ON services (client_id);
 CREATE INDEX IF NOT EXISTS bookings_client_idx  ON bookings (client_id);
 CREATE INDEX IF NOT EXISTS users_client_idx     ON users (client_id);