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/static/index.html

@@ -41,6 +41,7 @@
         <div class="persona-switcher" id="persona-switcher">
             <div class="name" id="persona-name">Inara</div>
             <div class="subtitle">Cortex · Local</div>
+            <div id="session-id"></div>
             <div class="persona-dropdown" id="persona-dropdown"></div>
         </div>
 
@@ -164,7 +165,6 @@
     </div>
 
     <div id="messages"></div>
-    <div id="session-id"></div>
 
     <div id="input-area">
         <!-- Mode select — compact dropdown, opens upward, MRU sorted -->