Feat: transcript retention (#123)

* feat(retention): prune old agent transcripts + panel-tunable setting

Agents write a {session-id}.jsonl per spawn under ~/.claude/projects; nothing
ever deleted them, so the operator's bind-mounted ~/.claude grew without bound.

Add a throttled orchestrator sweep that prunes agent-owned transcripts (the
shared -app dir + per-workspace dirs) older than a retention window — and ONLY
agent-owned dirs, never the operator's own Claude sessions (proven by the
temp-dir selection tests). The window is panel-tunable: a new system_settings
key-value table (migration 027) holds transcript_retention_days, read via
SettingsService with the roboco.config default (14d) as the fallback, exposed
through GET/PUT /api/settings. Panel wiring follows.

* feat(panel): add a panel-tunable transcript retention control

Wire the settings page to the /api/settings backend: a settings API client and
a self-contained Transcript Retention card (React Query) that loads
transcript_retention_days and saves it back, with client-side validation. The
existing settings controls are unchanged.

---------

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

panel/src/app/(dashboard)/settings/page.tsx

@@ -26,6 +26,7 @@ import {
 } from "lucide-react";
 import { toast } from "sonner";
 import { API_URL, WS_URL } from "@/lib/constants";
+import { TranscriptRetentionCard } from "@/components/settings/transcript-retention-card";
 
 export default function SettingsPage() {
   const { theme, setTheme } = useTheme();
@@ -183,6 +184,9 @@ export default function SettingsPage() {
         </CardContent>
       </Card>
 
+      {/* Transcript Retention (panel-tunable; persisted server-side) */}
+      <TranscriptRetentionCard />
+
       {/* Connection Info */}
       <Card>
         <CardHeader>