herdr phase 1a: missions runtime_kind + target_node schema

First slice of the second-runtime path. Missions now carry
runtime_kind ('zeroclaw' | 'local_herdr') + target_node_id (FK to
nodes) so the mission_orchestrator + phase executors can dispatch
differently depending on where the operator wants execution.

Migration:
  - 0055_missions_runtime_kind.sql — adds runtime_kind (NOT NULL
    DEFAULT 'zeroclaw' + CHECK), target_node_id (nullable FK ON
    DELETE SET NULL). All existing missions backfill to 'zeroclaw'
    so behavior is unchanged.
  - topology_runs also grows herdr_workspace_id / herdr_tab_id /
    herdr_pane_id text columns so a resumed run can reattach to the
    same Herdr pane instead of spawning a duplicate.

Code:
  - cm-db::repo::missions — Mission + NewMission carry the two new
    fields; all SELECTs updated; INSERT COALESCE-defaults
    runtime_kind to 'zeroclaw' when unspecified.
  - routes::missions::create — validates runtime_kind and requires
    target_node_id when kind='local_herdr' (400 otherwise).
  - lib/api/missions.ts — RuntimeKind type; Mission carries both;
    CreateMissionRequest optional fields.

Behavior is opt-in: no path exists yet to actually create a
local_herdr mission — that lands in Phase 1c (wizard picker). This
commit just makes the schema + validation in place so Phase 1b's
fleet_herdr dispatch module can key on it.

Tests: mission_orchestrator integration test still green.

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

@@ -30,6 +30,10 @@ pub struct Mission {
     pub status: String,
     pub description: Option<String>,
     pub config: Value,
+    /// 'zeroclaw' (default, headless) | 'local_herdr' (attended, fleet node)
+    pub runtime_kind: String,
+    /// FK → nodes(id); only relevant when runtime_kind = 'local_herdr'
+    pub target_node_id: Option<Uuid>,
     #[serde(with = "time::serde::rfc3339")]
     pub created_at: OffsetDateTime,
     #[serde(with = "time::serde::rfc3339")]
@@ -106,6 +110,9 @@ pub struct NewMission<'a> {
     pub schedule: Value,
     pub description: Option<&'a str>,
     pub config: Value,
+    /// Defaults to 'zeroclaw' when None.
+    pub runtime_kind: Option<&'a str>,
+    pub target_node_id: Option<Uuid>,
     pub phases: Vec<NewMissionPhase>,
 }
 
@@ -127,8 +134,10 @@ pub async fn insert(pool: &PgPool, m: NewMission<'_>) -> Result<Uuid, DbError> {
     sqlx::query(
         "INSERT INTO missions
            (id, workspace_id, title, template_kind, team_id,
-            team_template_id, repo_id, schedule, status, description, config)
-         VALUES ($1,$2,$3,$4,$5,$6,$7,$8,'draft',$9,$10)",
+            team_template_id, repo_id, schedule, status, description, config,
+            runtime_kind, target_node_id)
+         VALUES ($1,$2,$3,$4,$5,$6,$7,$8,'draft',$9,$10,
+                 COALESCE($11,'zeroclaw'),$12)",
     )
     .bind(mission_id)
     .bind(m.workspace_id)
@@ -140,6 +149,8 @@ pub async fn insert(pool: &PgPool, m: NewMission<'_>) -> Result<Uuid, DbError> {
     .bind(&m.schedule)
     .bind(m.description)
     .bind(&m.config)
+    .bind(m.runtime_kind)
+    .bind(m.target_node_id)
     .execute(&mut *tx)
     .await?;
 
@@ -169,7 +180,8 @@ pub async fn get(pool: &PgPool, id: Uuid, workspace_id: Uuid) -> Result<Option<M
     let row = sqlx::query(
         "SELECT id, workspace_id, title, template_kind, team_id,
                 team_template_id, repo_id, schedule, status,
-                description, config, created_at, updated_at, completed_at
+                description, config, runtime_kind, target_node_id,
+                created_at, updated_at, completed_at
          FROM missions WHERE id = $1 AND workspace_id = $2",
     )
     .bind(id)
@@ -188,6 +200,8 @@ pub async fn get(pool: &PgPool, id: Uuid, workspace_id: Uuid) -> Result<Option<M
         status: r.get("status"),
         description: r.get("description"),
         config: r.get("config"),
+        runtime_kind: r.get("runtime_kind"),
+        target_node_id: r.get("target_node_id"),
         created_at: r.get("created_at"),
         updated_at: r.get("updated_at"),
         completed_at: r.get("completed_at"),
@@ -204,7 +218,8 @@ pub async fn list_by_workspace(
     let rows = sqlx::query(
         "SELECT id, workspace_id, title, template_kind, team_id,
                 team_template_id, repo_id, schedule, status,
-                description, config, created_at, updated_at, completed_at
+                description, config, runtime_kind, target_node_id,
+                created_at, updated_at, completed_at
          FROM missions WHERE workspace_id = $1
          ORDER BY created_at DESC LIMIT $2",
     )
@@ -226,6 +241,8 @@ pub async fn list_by_workspace(
             status: r.get("status"),
             description: r.get("description"),
             config: r.get("config"),
+            runtime_kind: r.get("runtime_kind"),
+            target_node_id: r.get("target_node_id"),
             created_at: r.get("created_at"),
             updated_at: r.get("updated_at"),
             completed_at: r.get("completed_at"),