feat(drive): start implementation of drive

- add storage.drives
    - prepare migration phase
    - add created_by and updated_by on storage.folders

migrations/20260802000002_drives_not_null.sql

@@ -0,0 +1,108 @@
+-- ════════════════════════════════════════════════════════════════════════════
+-- D0 / M3 — Drive constraints: NOT NULL, FK, indexes
+-- ════════════════════════════════════════════════════════════════════════════
+-- Third of the D0 migration trio. Runs only after M2 (the backfill) has
+-- populated every folder/file row with a `drive_id`. This migration is
+-- the point of no easy rollback — once `drive_id` is NOT NULL and
+-- foreign-keyed to `storage.drives`, dropping the column requires the
+-- application code to first stop reading it.
+--
+-- What lands here:
+--   * NOT NULL on `storage.folders.drive_id` and `storage.files.drive_id`.
+--   * Foreign keys from both to `storage.drives(id)` with ON DELETE
+--     CASCADE (deleting a drive removes its tree — matches the
+--     post-D2 lifecycle plan).
+--   * Indexes on `drive_id` for both tables (hot path: list-by-drive,
+--     drive-aware Tantivy reseed, drive-quota counters).
+--
+-- The `user_id` column is intentionally left in place: dual-write during
+-- the D0 release cycle is the rollback safety net. D7 drops user_id once
+-- the new model has baked.
+
+-- ── 1. NOT NULL on drive_id ────────────────────────────────────────────────
+-- M2's post-flight check refused to commit if any row was missing
+-- drive_id, so this should never fail. The check at column promotion
+-- time is the belt; M2's pre-commit assertion was the suspenders.
+
+ALTER TABLE storage.folders
+    ALTER COLUMN drive_id SET NOT NULL;
+
+ALTER TABLE storage.files
+    ALTER COLUMN drive_id SET NOT NULL;
+
+
+-- ── 2. Foreign keys to storage.drives ──────────────────────────────────────
+-- ON DELETE CASCADE: when a drive is deleted (D3 ships the delete-drive
+-- flow), every folder and file row carrying that drive_id is removed in
+-- the same transaction. Trash retention does not apply — drive deletion
+-- is the explicit "I'm done with this storage" gesture.
+
+ALTER TABLE storage.folders
+    ADD CONSTRAINT folders_drive_id_fkey
+    FOREIGN KEY (drive_id) REFERENCES storage.drives(id) ON DELETE CASCADE;
+
+ALTER TABLE storage.files
+    ADD CONSTRAINT files_drive_id_fkey
+    FOREIGN KEY (drive_id) REFERENCES storage.drives(id) ON DELETE CASCADE;
+
+
+-- ── 3. Indexes on drive_id ─────────────────────────────────────────────────
+-- The hot path that ranks every drive-aware query: "list folders in
+-- drive X", "files in drive X for Tantivy reindex", "per-drive quota
+-- aggregation". The existing `user_id` indexes are kept during dual-
+-- write and dropped in D7 alongside the column.
+
+CREATE INDEX IF NOT EXISTS idx_folders_drive_id ON storage.folders (drive_id);
+CREATE INDEX IF NOT EXISTS idx_files_drive_id   ON storage.files   (drive_id);
+
+
+-- ── 4. Post-flight: confirm constraints landed ────────────────────────────
+-- Belt-and-suspenders verification that the NOT NULL + FK actually
+-- exist after the ALTERs above. Any failure here means PostgreSQL
+-- silently no-op'd one of the constraint changes, which would be a
+-- bug worth surfacing immediately.
+
+DO $BODY$
+DECLARE
+    folder_not_null  BOOLEAN;
+    file_not_null    BOOLEAN;
+    folder_fk_exists BOOLEAN;
+    file_fk_exists   BOOLEAN;
+BEGIN
+    SELECT NOT is_nullable::boolean INTO folder_not_null
+    FROM information_schema.columns
+    WHERE table_schema = 'storage'
+      AND table_name   = 'folders'
+      AND column_name  = 'drive_id';
+
+    SELECT NOT is_nullable::boolean INTO file_not_null
+    FROM information_schema.columns
+    WHERE table_schema = 'storage'
+      AND table_name   = 'files'
+      AND column_name  = 'drive_id';
+
+    SELECT EXISTS (
+        SELECT 1 FROM information_schema.table_constraints
+         WHERE table_schema    = 'storage'
+           AND table_name      = 'folders'
+           AND constraint_name = 'folders_drive_id_fkey'
+           AND constraint_type = 'FOREIGN KEY'
+    ) INTO folder_fk_exists;
+
+    SELECT EXISTS (
+        SELECT 1 FROM information_schema.table_constraints
+         WHERE table_schema    = 'storage'
+           AND table_name      = 'files'
+           AND constraint_name = 'files_drive_id_fkey'
+           AND constraint_type = 'FOREIGN KEY'
+    ) INTO file_fk_exists;
+
+    IF NOT folder_not_null OR NOT file_not_null
+       OR NOT folder_fk_exists OR NOT file_fk_exists THEN
+        RAISE EXCEPTION
+            'D0 M3 post-flight failed: '
+            'folder NOT NULL=%, file NOT NULL=%, folder FK=%, file FK=%. '
+            'All four must be true after this migration commits.',
+            folder_not_null, file_not_null, folder_fk_exists, file_fk_exists;
+    END IF;
+END $BODY$;