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>

tests/unit/services/test_settings_service.py

@@ -0,0 +1,56 @@
+"""Tests for SettingsService + setting validation."""
+
+from __future__ import annotations
+
+from typing import Any
+
+import pytest
+from roboco.services.settings import (
+    SettingValidationError,
+    get_settings_service,
+    validate_setting,
+)
+
+
+def test_validate_setting_rejects_unknown_key() -> None:
+    with pytest.raises(SettingValidationError):
+        validate_setting("not_a_real_setting", "x")
+
+
+def test_validate_retention_requires_positive_int() -> None:
+    validate_setting("transcript_retention_days", "7")  # ok, no raise
+    with pytest.raises(SettingValidationError):
+        validate_setting("transcript_retention_days", "0")
+    with pytest.raises(SettingValidationError):
+        validate_setting("transcript_retention_days", "abc")
+
+
+_DEFAULT_RETENTION = 14
+_NEW_RETENTION = 30
+
+
+@pytest.mark.asyncio
+async def test_get_int_returns_default_when_unset(db_session: Any) -> None:
+    svc = get_settings_service(db_session)
+    assert (
+        await svc.get_int("transcript_retention_days", _DEFAULT_RETENTION)
+        == _DEFAULT_RETENTION
+    )
+
+
+@pytest.mark.asyncio
+async def test_set_then_get_roundtrips(db_session: Any) -> None:
+    svc = get_settings_service(db_session)
+    await svc.set("transcript_retention_days", str(_NEW_RETENTION))
+    assert (
+        await svc.get_int("transcript_retention_days", _DEFAULT_RETENTION)
+        == _NEW_RETENTION
+    )
+    assert (await svc.all())["transcript_retention_days"] == str(_NEW_RETENTION)
+
+
+@pytest.mark.asyncio
+async def test_set_rejects_invalid_value(db_session: Any) -> None:
+    svc = get_settings_service(db_session)
+    with pytest.raises(SettingValidationError):
+        await svc.set("transcript_retention_days", "-5")