feat: expand MetalCircle app and privacy controls

db/migrations/12_user_blocks.sql

@@ -0,0 +1,10 @@
+CREATE TABLE IF NOT EXISTS user_blocks (
+    blocker_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    blocked_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    PRIMARY KEY (blocker_id, blocked_id),
+    CHECK (blocker_id <> blocked_id)
+);
+
+CREATE INDEX IF NOT EXISTS idx_user_blocks_blocked
+ON user_blocks (blocked_id, blocker_id);