feat: reasoning token budget + session name in header

- reasoning_budget_tokens: optional int field on local_openai models;
  when set, injects {"reasoning": {"budget_tokens": N}} via extra_body
  into every OpenRouter API call (both tool-loop and confirmation-gate
  rounds). Field exposed in the model edit form in Settings.

- session name moved from standalone full-row div between #messages
  and #input-area into the persona-switcher block in the header, as a
  third dim line under "Cortex · Local". Collapses when empty via
  :empty CSS. No JS changes required.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/openai_orchestrator.py

@@ -287,6 +287,9 @@ async def _run_from_messages(
         if active_tools:
             call_kwargs["tools"] = active_tools
             call_kwargs["tool_choice"] = "auto"
+        reasoning_budget = (model_cfg or {}).get("reasoning_budget_tokens")
+        if reasoning_budget:
+            call_kwargs["extra_body"] = {"reasoning": {"budget_tokens": reasoning_budget}}
         response = await _chat_with_retry(client, **call_kwargs)
 
         choice = response.choices[0]
@@ -346,6 +349,8 @@ async def _run_from_messages(
                 conf_call: dict = {"model": model_name, "messages": messages, "tool_choice": "none"}
                 if active_tools:
                     conf_call["tools"] = active_tools
+                if reasoning_budget:
+                    conf_call["extra_body"] = {"reasoning": {"budget_tokens": reasoning_budget}}
                 conf_resp = await _chat_with_retry(client, **conf_call)
                 final_response = conf_resp.choices[0].message.content or (
                     "This action requires your explicit confirmation before it can proceed."