feat: add workflow studio and postgres support

migrations_pg/20260522000001_user_announcements.sql

@@ -0,0 +1,33 @@
+-- Admin-authored announcements for normal users.
+
+CREATE TABLE IF NOT EXISTS user_announcements (
+    id           BIGSERIAL PRIMARY KEY,
+    title        TEXT NOT NULL,
+    content      TEXT NOT NULL,
+    level        TEXT NOT NULL DEFAULT 'info',
+    status       TEXT NOT NULL DEFAULT 'published',
+    audience     TEXT NOT NULL DEFAULT 'all',
+    starts_at    TEXT,
+    ends_at      TEXT,
+    created_at   TEXT NOT NULL DEFAULT (CURRENT_TIMESTAMP::TEXT),
+    updated_at   TEXT NOT NULL DEFAULT (CURRENT_TIMESTAMP::TEXT),
+    published_at TEXT
+);
+
+CREATE INDEX IF NOT EXISTS user_announcements_status_created_at_idx
+    ON user_announcements (status, created_at);
+
+CREATE INDEX IF NOT EXISTS user_announcements_active_window_idx
+    ON user_announcements (starts_at, ends_at);
+
+CREATE TABLE IF NOT EXISTS user_announcement_reads (
+    announcement_id BIGINT NOT NULL,
+    user_id         BIGINT NOT NULL,
+    read_at         TEXT NOT NULL DEFAULT (CURRENT_TIMESTAMP::TEXT),
+    PRIMARY KEY (announcement_id, user_id),
+    FOREIGN KEY (announcement_id) REFERENCES user_announcements(id) ON DELETE CASCADE,
+    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
+);
+
+CREATE INDEX IF NOT EXISTS user_announcement_reads_user_id_idx
+    ON user_announcement_reads (user_id);