Add model selection, dashboard chat input, and model warming

- Add GET /api/chat/ps and POST /api/chat/warm endpoints for hot model
  visibility and pre-loading
- Extend PATCH /api/chat/conversations/:id to accept model in addition
  to title
- Add ModelSelector component with hot/cold indicators from Ollama /api/ps
- Add DashboardChatInput component (model selector + note picker + textarea)
  replacing the simple "New Chat" button on the dashboard
- Add model selector dropdown to ChatView header, persisted per-conversation
- Warm default model on dashboard mount via fire-and-forget background task
- Configure Ollama with OLLAMA_MAX_LOADED_MODELS=2 and OLLAMA_KEEP_ALIVE=30m
- Always-visible edit buttons on NoteCard/TaskCard (remove hover-only behavior)

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

frontend/src/components/NoteCard.vue

@@ -68,28 +68,19 @@ function goEdit() {
 }
 .btn-edit {
   flex-shrink: 0;
-  padding: 0.2rem 0.5rem;
-  font-size: 0.75rem;
-  background: transparent;
-  color: var(--color-text-muted);
+  padding: 0.25rem 0.6rem;
+  font-size: 0.8rem;
+  background: var(--color-bg-card);
+  color: var(--color-text-secondary);
   border: 1px solid var(--color-border);
   border-radius: var(--radius-sm);
   cursor: pointer;
-  opacity: 0;
-  transition: opacity 0.15s, color 0.15s, border-color 0.15s;
-}
-.note-card:hover .btn-edit {
-  opacity: 1;
+  transition: color 0.15s, border-color 0.15s, background 0.15s;
 }
 .btn-edit:hover {
   color: var(--color-primary);
   border-color: var(--color-primary);
 }
-@media (hover: none) {
-  .btn-edit {
-    opacity: 1;
-  }
-}
 .note-preview {
   margin: 0 0 0.5rem;
   color: var(--color-text-secondary);