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>

roboco/config.py

@@ -244,6 +244,37 @@ class Settings(BaseSettings):
         ),
     )
 
+    # ==========================================================================
+    # Transcript retention (agent Claude Code transcripts under ~/.claude)
+    # ==========================================================================
+    transcript_retention_days: int = Field(
+        default=14,
+        ge=1,
+        description=(
+            "Default retention window, in days, for agent Claude Code "
+            "transcripts (the *.jsonl files agents write under "
+            "~/.claude/projects). A background sweep prunes agent-owned "
+            "transcripts older than this. Panel-editable: a stored "
+            "`transcript_retention_days` system setting overrides this default "
+            "when present; this is the fallback used before one is set."
+        ),
+    )
+    transcript_prune_enabled: bool = Field(
+        default=True,
+        description=(
+            "Whether the orchestrator background sweep prunes old agent "
+            "transcripts. Disable to keep every transcript indefinitely."
+        ),
+    )
+    transcript_prune_interval_seconds: int = Field(
+        default=3600,
+        ge=300,
+        description=(
+            "Minimum seconds between transcript-retention prune passes. The "
+            "prune is age-based (days), so it need not run more than hourly."
+        ),
+    )
+
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