Add admin LLM model setting; rename Pi to LLM in the UI; drop table Review column

- New server/llm.js consolidates ModelRuntime + model selection: admin
  setting (app_settings.llm_model) > LLM_MODEL/PREFILL_MODEL env > first
  available; used by both prefill and roast evaluation
- GET/PUT /api/admin/llm lists configured models and stores the choice
  (validated against the list; empty = auto; audited); admin page gains
  an LLM section with a model picker
- All user-facing 'Pi agent' wording is now 'LLM'; no_model error message
  no longer references the pi CLI
- /roasts table: Review column removed (review lives in the detail view)

Co-Authored-By: Claude Fable 5 <[email protected]>

public/index.html

@@ -227,7 +227,7 @@
         <h4 style="margin:0 0 6px">Log a finished roast</h4>
         <p class="field-note" style="margin-top:0">
           Upload the actual roast's .alog to attach it to this plan — you can
-          upload several. The Pi agent reviews each one in the background.
+          upload several. The LLM reviews each one in the background.
         </p>
         <label class="filebtn primary-btn"
           >Upload finished roast(s)<input