research: publish approval gate + explicit state transitions

Fourth commit of the Research + Loops arc. Completes the state machine
for research topics with the publish approval gate the spec asked for.

Migration 0032 — research_publish_approvals
  Dedicated small table (id, workspace_id, topic_id, requested_by,
  status, decided_by/at, created_at). Keeping it separate from the
  existing `approvals` table (0001) because that one is tightly coupled
  to gated tool calls inside an agent run — session_key + run_id +
  action_type + category + payload + preview + requested_by_agent, all
  NOT NULL. Forcing those nullable would ripple through cm_safety;
  cleaner to give publish approvals their own two-transition state
  machine.

New endpoints
  POST /api/research/:id/submit-review               processing → reviewing
                                                     (v1 caller-driven; the
                                                     orchestrator hook comes
                                                     when we wire actual runs)
  POST /api/research/:id/request-publish             creates a pending
                                                     approval. Rejects with
                                                     409 if the topic already
                                                     has one open.
  GET  /api/research/publish-approvals               list workspace's pending
  POST /api/research/publish-approvals/:id/approve   flips approval to
                                                     approved + transitions
                                                     the topic
                                                     reviewing → publishing
                                                     (which stamps
                                                     published_at)
  POST /api/research/publish-approvals/:id/reject    stays in reviewing; new
                                                     requests allowed

The approve/reject write is an atomic UPDATE ... WHERE status = 'pending';
the decide() repo function returns whether the caller won the race so
concurrent double-approves collapse to a single topic transition.

State machine after this commit:
  standby ─POST /start─▶ processing ─POST /submit-review─▶ reviewing
    ─POST /request-publish + approve─▶ publishing ─(future: artifact
    assembly)─▶ published

.sqlx/query-208b41dc1f8cb9f6ff46ce6a01d15c2ddbf604d6a4062f95b1eb99720c244ff2.json

@@ -0,0 +1,17 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "INSERT INTO research_publish_approvals\n            (id, workspace_id, topic_id, requested_by, status)\n         VALUES ($1, $2, $3, $4, 'pending')",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Uuid",
+        "Uuid",
+        "Uuid",
+        "Uuid"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "208b41dc1f8cb9f6ff46ce6a01d15c2ddbf604d6a4062f95b1eb99720c244ff2"
+}