chore: greenfield migrations — remove user/role tables, add api_keys, drop bootstrap_token

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main/resources/db/migration/V004__create_api_keys.sql

@@ -0,0 +1,12 @@
+CREATE TABLE api_keys (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    environment_id UUID NOT NULL REFERENCES environments(id) ON DELETE CASCADE,
+    key_hash VARCHAR(64) NOT NULL,
+    key_prefix VARCHAR(12) NOT NULL,
+    status VARCHAR(20) NOT NULL DEFAULT 'ACTIVE',
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    revoked_at TIMESTAMPTZ
+);
+
+CREATE INDEX idx_api_keys_env ON api_keys(environment_id);
+CREATE INDEX idx_api_keys_hash ON api_keys(key_hash);