feat: series-aware schedule edits + waitlist ledger removal (M32)

PATCH /v1/catalog/class-schedules/:id patches a recurring rule and,
with applyToFuture, retimes materialized future sessions to the new
local start time on their existing dates — moving confirmed and
waitlisted bookings with them and re-arming reminders. Zones-page
schedule rows gain an inline editor (CS/EN).

Also drops the vestigial waitlist_entries table (migration 00020):
positions derive from bookings.created_at, so the ledger was written
but never read.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/migrations/00020_drop_waitlist_entries.sql

@@ -0,0 +1,18 @@
+-- +goose Up
+-- waitlist_entries was written on waitlist join/promotion but never read:
+-- every displayed position derives from bookings.created_at ordering via
+-- GetWaitlistPosition. Dropping the dead ledger rather than keeping a
+-- write-only table that implies state it does not hold.
+DROP TABLE IF EXISTS waitlist_entries;
+
+-- +goose Down
+CREATE TABLE IF NOT EXISTS waitlist_entries (
+  id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+  tenant_id uuid NOT NULL REFERENCES tenants(id) ON DELETE CASCADE,
+  class_session_id uuid NOT NULL REFERENCES class_sessions(id) ON DELETE CASCADE,
+  customer_name text NOT NULL,
+  customer_email text NOT NULL,
+  position integer NOT NULL,
+  status text NOT NULL DEFAULT 'pending',
+  created_at timestamptz NOT NULL DEFAULT now()
+);