mission canvas: add / edit / delete toolbar controls

Top-right toolbar grows three CRUD controls per your request:

  - Plus (always visible) — opens MissionWizard, selects the new
    mission on create
  - Pencil (draft-only) — opens EditMissionModal for title +
    description; PATCHes /api/missions/{id}
  - Trash (always visible) — window.confirm then DELETEs; sidebar
    selection clears via new onDeleted callback

Backend:
  - cm-db::repo::missions::update_meta(id, ws, title?, description?)
    — COALESCE-based partial patch
  - cm-db::repo::missions::delete(id, ws) — hard delete, cascades
    via FKs on phases/tasks/artifacts/benchmark_snapshots
  - PATCH /api/missions/{id} (draft-only) + DELETE /api/missions/{id}

Frontend:
  - lib/api/missions — updateMission + deleteMission clients
  - MissionCanvas — three toolbar buttons, EditMissionModal
    (title + textarea for description), local wizard state
  - Dashboard — passes onSelect + onDeleted so sidebar reacts to
    create + delete without stale selection

Edit is draft-only (backend enforces + button hidden past draft) so
in-flight missions can't have their brief mutated out from under
running agents. Delete is unconditional — operator responsibility to
Cancel first if a run is live.

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

@@ -252,6 +252,47 @@ pub async fn set_description(
     Ok(())
 }
 
+/// Patch title + description in one shot. Either field `None` = leave
+/// as-is (uses COALESCE so partial edits don't clobber the other).
+pub async fn update_meta(
+    pool: &PgPool,
+    id: Uuid,
+    workspace_id: Uuid,
+    title: Option<&str>,
+    description: Option<&str>,
+) -> Result<(), DbError> {
+    sqlx::query(
+        "UPDATE missions
+            SET title       = COALESCE($3, title),
+                description = COALESCE($4, description),
+                updated_at  = now()
+          WHERE id = $1 AND workspace_id = $2",
+    )
+    .bind(id)
+    .bind(workspace_id)
+    .bind(title)
+    .bind(description)
+    .execute(pool)
+    .await?;
+    Ok(())
+}
+
+/// Hard-delete a mission. Cascades via FKs on mission_phases /
+/// mission_tasks / mission_artifacts / benchmark_snapshots (all
+/// declared ON DELETE CASCADE in 0047).
+pub async fn delete(
+    pool: &PgPool,
+    id: Uuid,
+    workspace_id: Uuid,
+) -> Result<u64, DbError> {
+    let r = sqlx::query("DELETE FROM missions WHERE id = $1 AND workspace_id = $2")
+        .bind(id)
+        .bind(workspace_id)
+        .execute(pool)
+        .await?;
+    Ok(r.rows_affected())
+}
+
 pub async fn set_status(
     pool: &PgPool,
     id: Uuid,