Feature 04 task 5: Async job runner and GET /api/v1/jobs/{id} (#29)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>
Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>

migrations/0003_jobs_status.sql

@@ -0,0 +1,32 @@
+-- 0003_jobs_status: jobs.status becomes queued, running, succeeded, failed,
+-- the states the job runner (internal/jobs) reports. SQLite cannot change a
+-- CHECK in place, so the table is rebuilt: create the new table, copy every
+-- row, drop the old one and rename. Nothing references jobs and it has no
+-- indexes or triggers, so the rebuild touches no other schema object. Rows
+-- written under the 0001 values are mapped (pending -> queued,
+-- done -> succeeded) so the copy cannot fail on an existing database.
+
+CREATE TABLE jobs_new (
+	id          TEXT NOT NULL PRIMARY KEY,
+	kind        TEXT NOT NULL,
+	status      TEXT NOT NULL CHECK (status IN ('queued', 'running', 'succeeded', 'failed')),
+	payload     TEXT NOT NULL, -- JSON
+	result      TEXT,          -- JSON, written progressively
+	error       TEXT,
+	started_at  TEXT,
+	finished_at TEXT,
+	created_at  TEXT NOT NULL,
+	updated_at  TEXT NOT NULL
+);
+
+INSERT INTO jobs_new (id, kind, status, payload, result, error, started_at, finished_at, created_at, updated_at)
+SELECT
+	id,
+	kind,
+	CASE status WHEN 'pending' THEN 'queued' WHEN 'done' THEN 'succeeded' ELSE status END,
+	payload, result, error, started_at, finished_at, created_at, updated_at
+FROM jobs;
+
+DROP TABLE jobs;
+
+ALTER TABLE jobs_new RENAME TO jobs;