loops: bridge research artifact into loop iterations (option C + b)

The bridge lets a coding loop "consume" an integrations research
artifact one INT-XX item per iteration. Options b (order-sequential
iteration) and C (snapshot in task_template + save the pointer for
future refresh) from the design discussion.

Migration 0042 — three new loops columns:
- source_research_topic_id — nullable pointer to research_topics.
- consumed_int_ids TEXT[]   — INT-XX ids the loop has completed.
  Advances when topology_worker parses "COMPLETED: INT-<NN>" markers
  from the run's final output (wired in a follow-up commit).
- current_int_index INT     — monotonic pointer for order-sequential
  iteration. Coordinator addresses INT-<current+1> unless prereqs are
  unmet, in which case it works on the smallest unblocking INT-XX and
  logs the reorder rationale.

Backend:
- cm_db::repo::loops::set_source_research_topic — bind/unbind pointer.
- cm_db::repo::loops::source_research_context   — read pointer + state.
- routes::loops::compose_iteration_task         — new caller-side helper
  that reads the pointer, fetches the topic's latest research_outcome,
  and prepends the artifact + focus instruction to task_template.
- run_now + webhook_receive both pass task_template through
  compose_iteration_task before enqueue. Standalone loops (no pointer)
  behave identically to before.
- CreateLoopRequest accepts `source_research_topic_id`, ownership-
  checked via research_topics::get before persist.

Frontend:
- New ResearchArtifactPicker modal — lists published topics, fetches
  the artifact on pick, returns (topic_id, markdown) to caller.
- LoopsWizard task_template step gains "Import from research artifact"
  button (right-aligned). Click opens the picker. On pick: task
  populates with the artifact markdown, pointer saved, textarea
  expands to 8 rows, small info strip shows "Loop is bound to topic
  <id>. Each iteration will focus on the next unconsumed INT-XX."
- Unlink button reverts to standalone loop mode.

Follow-up (next commit):
- topology_worker completion hook — parse "COMPLETED: INT-<NN>" out
  of the run's final output + update consumed_int_ids +
  current_int_index atomically. Without this, current_int_index stays
  at 0 forever and every iteration works on the same INT.
- Loop card refresh button — re-read source topic's latest outcome
  (useful after a reject-with-revision cycle on the source topic).

crates/cm-db/src/repo/loops.rs

@@ -247,6 +247,59 @@ pub async fn set_zeroclaw_container(
     Ok(())
 }
 
+/// Bind (or unbind) a loop's source research topic. When set, the loop's
+/// enqueue path prepends the topic's latest artifact + a "focus on the
+/// next unconsumed INT" instruction to the coordinator task (option b,
+/// order-sequential iteration).
+pub async fn set_source_research_topic(
+    pool: &PgPool,
+    loop_id: Uuid,
+    workspace_id: Uuid,
+    source: Option<Uuid>,
+) -> Result<(), DbError> {
+    sqlx::query(
+        "UPDATE loops
+            SET source_research_topic_id = $3, updated_at = now()
+          WHERE id = $1 AND workspace_id = $2",
+    )
+    .bind(loop_id)
+    .bind(workspace_id)
+    .bind(source)
+    .execute(pool)
+    .await?;
+    Ok(())
+}
+
+/// Read a loop's source research topic id + consumed INT ids +
+/// current index. Used by the enqueue path when building the
+/// coordinator task string. Missing rows / NULL columns return None
+/// so the caller can fall back to the plain task_template.
+pub async fn source_research_context(
+    pool: &PgPool,
+    loop_id: Uuid,
+) -> Result<Option<(Uuid, Vec<String>, i32)>, DbError> {
+    use sqlx::Row;
+    let row = sqlx::query(
+        "SELECT source_research_topic_id, consumed_int_ids, current_int_index
+           FROM loops
+          WHERE id = $1",
+    )
+    .bind(loop_id)
+    .fetch_optional(pool)
+    .await?;
+    Ok(row.and_then(|r| {
+        let topic = r
+            .try_get::<Option<Uuid>, _>("source_research_topic_id")
+            .ok()
+            .flatten()?;
+        let consumed = r
+            .try_get::<Vec<String>, _>("consumed_int_ids")
+            .unwrap_or_default();
+        let idx = r.try_get::<i32, _>("current_int_index").unwrap_or(0);
+        Some((topic, consumed, idx))
+    }))
+}
+
 /// Read the per-loop gateway URL (or None if the loop hasn't spawned a
 /// container yet). Used by `topology_worker` to prefer the isolated
 /// daemon over the workspace-wide one.