feat(soul): add sessions layer, MCP connectors, conversation continuity fix

- sessions.el: new sessions module with session management and approval gate
- routes.el: wire /api/sessions routes (list, get, create, approve, tool_result)
- chat.el: thread-aware activation — short messages anchor to last reply
  before engram compilation so follow-ups stay on-topic
- chat.el: agentic path tracks per-session history (session_hist_{id})
  instead of shared conv_history, seeding each turn with prior context
- chat.el: add call_neuron_mcp, dispatch_tool, is_builtin_tool, next_bridge_id
  agentic_loop, bridge_save, agentic_resume, handle_tool_result
- dist/soul: rebuild with all of the above

dist/semantics.elh

@@ -1,4 +1,4 @@
-// auto-generated by elc --emit-header — do not edit
+// auto-generated by elc --emit-header - do not edit
 extern fn sem_frame(intent: String, subject: String, obj: String, modifiers: String) -> Any
 extern fn sem_frame_lang(intent: String, subject: String, obj: String, modifiers: String, lang_code: String) -> Any
 extern fn sem_frame_simple(intent: String, subject: String) -> Any