feat: migrate editor sequences schema into auto-run migrations directory

Moved from schema_patch_editor.sql. All statements are idempotent
(IF NOT EXISTS / DO $$ BEGIN blocks) so safe to re-apply.

services/mam-api/src/db/migrations/003-editor-sequences.sql

@@ -0,0 +1,74 @@
+-- Wild Dragon MAM – Editor sequences
+-- Idempotent: safe to re-run (IF NOT EXISTS / DO $$ BEGIN guards throughout)
+
+-- Named timelines within a project (multiple per project, like Premiere)
+CREATE TABLE IF NOT EXISTS sequences (
+  id          UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
+  project_id  UUID NOT NULL REFERENCES projects ON DELETE CASCADE,
+  name        TEXT NOT NULL DEFAULT 'Sequence 1',
+  frame_rate  NUMERIC(6,3) NOT NULL DEFAULT 59.94,
+  width       INTEGER NOT NULL DEFAULT 1920,
+  height      INTEGER NOT NULL DEFAULT 1080,
+  created_at  TIMESTAMPTZ DEFAULT NOW(),
+  updated_at  TIMESTAMPTZ DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_sequences_project_id ON sequences(project_id);
+CREATE INDEX IF NOT EXISTS idx_sequences_updated_at ON sequences(updated_at DESC);
+
+-- Clips placed on a sequence timeline
+CREATE TABLE IF NOT EXISTS sequence_clips (
+  id                   UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
+  sequence_id          UUID NOT NULL REFERENCES sequences ON DELETE CASCADE,
+  asset_id             UUID NOT NULL REFERENCES assets ON DELETE CASCADE,
+  track                INTEGER NOT NULL DEFAULT 0 CHECK (track >= 0),
+  -- track encoding: 0=V1, 1=V2, 100=A1, 101=A2
+  timeline_in_frames   BIGINT NOT NULL,
+  timeline_out_frames  BIGINT NOT NULL,
+  source_in_frames     BIGINT NOT NULL DEFAULT 0,
+  source_out_frames    BIGINT NOT NULL,
+  created_at           TIMESTAMPTZ DEFAULT NOW(),
+  updated_at           TIMESTAMPTZ DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_sequence_clips_sequence_id    ON sequence_clips(sequence_id);
+CREATE INDEX IF NOT EXISTS idx_sequence_clips_track_position ON sequence_clips(sequence_id, track, timeline_in_frames);
+CREATE INDEX IF NOT EXISTS idx_sequence_clips_asset_id       ON sequence_clips(asset_id);
+
+-- Unique sequence name per project
+DO $$ BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM pg_constraint
+    WHERE conname = 'uq_sequences_project_name' AND conrelid = 'sequences'::regclass
+  ) THEN
+    ALTER TABLE sequences ADD CONSTRAINT uq_sequences_project_name UNIQUE (project_id, name);
+  END IF;
+END $$;
+
+-- Timeline range constraints
+DO $$ BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM pg_constraint
+    WHERE conname = 'chk_timeline_range' AND conrelid = 'sequence_clips'::regclass
+  ) THEN
+    ALTER TABLE sequence_clips ADD CONSTRAINT chk_timeline_range CHECK (timeline_out_frames > timeline_in_frames);
+  END IF;
+END $$;
+
+DO $$ BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM pg_constraint
+    WHERE conname = 'chk_source_range' AND conrelid = 'sequence_clips'::regclass
+  ) THEN
+    ALTER TABLE sequence_clips ADD CONSTRAINT chk_source_range CHECK (source_out_frames > source_in_frames);
+  END IF;
+END $$;
+
+DO $$ BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM pg_constraint
+    WHERE conname = 'chk_track_valid' AND conrelid = 'sequence_clips'::regclass
+  ) THEN
+    ALTER TABLE sequence_clips ADD CONSTRAINT chk_track_valid CHECK (track >= 0);
+  END IF;
+END $$;