feat(bookmarks): api+store — per-user CRUD, owner-scoped 404, percent-ordered list

backend/internal/db/schema.sql

@@ -19,3 +19,11 @@ CREATE TABLE IF NOT EXISTS reading_progress (
   locator JSONB NOT NULL DEFAULT '{}', percent DOUBLE PRECISION NOT NULL DEFAULT 0,
   updated_at TIMESTAMPTZ NOT NULL DEFAULT now(),
   PRIMARY KEY (user_id, library_id, book_path));
+CREATE TABLE IF NOT EXISTS bookmarks (
+  id BIGSERIAL PRIMARY KEY,
+  user_id BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+  library_id BIGINT NOT NULL, book_path TEXT NOT NULL,
+  locator JSONB NOT NULL, percent DOUBLE PRECISION NOT NULL DEFAULT 0,
+  note TEXT NOT NULL DEFAULT '',
+  created_at TIMESTAMPTZ NOT NULL DEFAULT now());
+CREATE INDEX IF NOT EXISTS bookmarks_user_book_idx ON bookmarks (user_id, library_id, book_path);