feat(jobs): migration 0005 + errs codes for jobs module

migrations/0005_jobs.down.sql

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+ALTER TABLE workspace_worktrees DROP COLUMN IF EXISTS prune_warning_at;
+DROP TABLE IF EXISTS jobs;

migrations/0005_jobs.up.sql

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+-- ============ jobs（DB-backed 事件型任务） ============
+CREATE TABLE jobs (
+  id            UUID PRIMARY KEY,
+  type          TEXT NOT NULL,
+  payload       JSONB NOT NULL DEFAULT '{}'::jsonb,
+  status        TEXT NOT NULL DEFAULT 'pending',
+  scheduled_at  TIMESTAMPTZ NOT NULL DEFAULT now(),
+  attempts      INT  NOT NULL DEFAULT 0,
+  max_attempts  INT  NOT NULL DEFAULT 5,
+  leased_at     TIMESTAMPTZ,
+  leased_by     TEXT,
+  last_error    TEXT,
+  completed_at  TIMESTAMPTZ,
+  created_at    TIMESTAMPTZ NOT NULL DEFAULT now(),
+  updated_at    TIMESTAMPTZ NOT NULL DEFAULT now(),
+  CONSTRAINT jobs_status_check CHECK (status IN ('pending','running','completed','dead'))
+);
+CREATE INDEX idx_jobs_pickup ON jobs(scheduled_at, status) WHERE status = 'pending';
+CREATE INDEX idx_jobs_lease  ON jobs(leased_at) WHERE status = 'running';
+CREATE INDEX idx_jobs_purge  ON jobs(completed_at) WHERE status IN ('completed', 'dead');
+
+-- ============ ALTER workspace_worktrees: add prune_warning_at ============
+ALTER TABLE workspace_worktrees
+  ADD COLUMN prune_warning_at TIMESTAMPTZ;