Output tool via Arc<Mutex<Subconscious>> closure — complete

ToolHandler is now Arc<dyn Fn(...)> supporting closures that capture
state. The output tool is created during init_output_tool() as a
closure capturing Arc<Mutex<Subconscious>>, writing directly to
Subconscious.state. No more POC_AGENT_OUTPUT_DIR filesystem hack.

- All tool handlers wrapped in Arc::new()
- Tool is Clone (not Copy) — .copied() → .cloned()
- Subconscious wrapped in Arc<Mutex<>> on Mind
- Dead filesystem-based output() function removed
- memory_tools returns 11 items (output removed from static list)

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/subconscious/digest.rs

@@ -1,3 +1,4 @@
+use std::sync::Arc;
 // Episodic digest generation: daily, weekly, monthly, auto
 //
 // Three digest levels form a temporal hierarchy: daily digests summarize