feat: session rename UX overhaul

- Edit button (✎) moved to left of row, separated from delete (×)
- Clicking ✎ hides name/meta/delete and expands input to full row width
- Button changes to ✓ (accent color) while editing
- Enter or ✓ click = save; Escape = cancel without saving
- Removed accidental-save-on-blur behavior
- Edit button: 30% opacity at rest, 75% on row hover, 100% on direct hover
- Touch devices: edit button always at 60% opacity (no hover to reveal it)

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

cortex/static/style.css

@@ -320,7 +320,7 @@
         }
         .session-delete-btn:hover { color: #e06c75; }
 
-        .session-rename-btn {
+        .session-edit-btn {
             background: none;
             border: none;
             color: var(--muted);
@@ -330,13 +330,30 @@
             cursor: pointer;
             border-radius: 3px;
             flex-shrink: 0;
-            opacity: 0.4;
+            opacity: 0.3;
             transition: opacity 0.15s, color 0.15s;
             min-width: 24px;
             text-align: center;
         }
-        .session-item:hover .session-rename-btn { opacity: 1; }
-        .session-rename-btn:hover { color: var(--accent); }
+        .session-item:hover .session-edit-btn { opacity: 0.75; }
+        .session-edit-btn:hover { color: var(--accent); opacity: 1; }
+
+        .session-save-btn {
+            background: none;
+            border: none;
+            color: var(--accent);
+            font-size: 1rem;
+            font-weight: bold;
+            line-height: 1;
+            padding: 2px 6px;
+            cursor: pointer;
+            border-radius: 3px;
+            flex-shrink: 0;
+            min-width: 24px;
+            text-align: center;
+            transition: opacity 0.15s;
+        }
+        .session-save-btn:hover { opacity: 0.75; }
 
         .session-rename-input {
             flex: 1;
@@ -1609,6 +1626,9 @@
                 min-width: 36px;
                 min-height: 36px;
             }
+
+            /* On touch: edit button always fully visible (no hover to reveal it) */
+            .session-edit-btn { opacity: 0.6; }
         }
 
         @media (max-width: 380px) {