feat: introduce Forever Mode (Sisyphus, Confucius, and Bicameral Voice)

- Sisyphus: auto-resume timer with schedule_work tool
- Confucius: built-in sub-agent for knowledge consolidation before compression
- Hippocampus: in-memory short-term memory via background micro-consolidation
- Bicameral Voice: proactive knowledge alignment on user input
- Archive compression mode for long-running sessions
- Onboarding dialog for first-time Forever Mode setup
- Refresh system instruction per turn so hippocampus reaches the model

docs/reference/configuration.md

@@ -175,6 +175,11 @@ their corresponding top-level category object in your `settings.json` file.
   - **Description:** Minimum retention period (safety limit, defaults to "1d")
   - **Default:** `"1d"`
 
+- **`general.sessionRetention.warningAcknowledged`** (boolean):
+  - **Description:** Whether the user has acknowledged the session retention
+    warning
+  - **Default:** `false`
+
 #### `output`
 
 - **`output.format`** (enum):