loops: repo picker + agent/team/org staffing + sidebar edit/delete

Adds the missing pieces the wizard needed and the sidebar controls
around it:

- LoopsWizard is now a 6-step flow (identity → repo → task/topology
  → triggers → repeat → assign agents) plus the existing secrets
  card. ResearchWizard picks up the same repo step and a hard gate
  when the workspace has zero agents.
- New LoopStaffingStep with three tabs — Individual / Team /
  Organization — that mix freely per loop; selections persist via
  new loop_agents / loop_teams / loop_orgs join tables (0035
  migration), each cascading on loop_id so hard-delete stays a
  single-row DELETE.
- Backend CreateLoopRequest / UpdateLoopRequest accept the three
  lists and apply_staffing does a transactional replace-all;
  list_loops / get_loop hydrate the lists via a flattened
  LoopWithStaffing response.
- LoopsList sidebar gains per-row enable/disable, edit (reopens the
  wizard prefilled with the current loop, PATCHes on submit), and
  delete with an inline confirm.
- NoAgentsGate blocks launching a loop or research topic from a
  workspace with no roster; the sidebar `+` buttons also disable
  with a tooltip pointing at the TEAM tier.

Not yet wired: the run driver still fills role slots from the
workspace-wide pool; teaching enqueue_iteration to prefer
loop_agents/loop_teams/loop_orgs is a follow-up.

frontend/src/components/dashboard/ResearchList.tsx

@@ -99,17 +99,25 @@ export function ResearchList({
         <button
           type="button"
           onClick={() => setWizardOpen(true)}
-          title="New research topic"
+          disabled={agents.length === 0}
+          title={
+            agents.length === 0
+              ? "Add an agent to your roster first"
+              : "New research topic"
+          }
           aria-label="New research topic"
           style={{
             flex: "none",
             width: 34,
             height: 34,
             borderRadius: 9,
-            border: "1px dashed rgba(255,111,97,.4)",
-            background: "rgba(255,111,97,.06)",
-            color: "#ff6f61",
-            cursor: "pointer",
+            border: `1px dashed ${agents.length === 0 ? "rgba(255,255,255,.14)" : "rgba(255,111,97,.4)"}`,
+            background:
+              agents.length === 0
+                ? "rgba(255,255,255,.02)"
+                : "rgba(255,111,97,.06)",
+            color: agents.length === 0 ? "#5a5a62" : "#ff6f61",
+            cursor: agents.length === 0 ? "not-allowed" : "pointer",
             display: "inline-flex",
             alignItems: "center",
             justifyContent: "center",