editor: resizable rail, Esc closes panel, dev tab remembered

Rail gets a drag handle on its edge (240-640px, width persisted like
the rest of the panel state). Escape now closes the panel as the last
step of its chain (dialog > inline > selection > panel). The dev panel
remembers its tab across reloads. Panel toggle button title notes the
Esc shortcut. Harness covers resize/persist, Esc-close and dev tab.

🤖 Generated with Codebuff
Co-Authored-By: Codebuff <noreply@codebuff.com>

src/ui/styles.css

@@ -228,6 +228,9 @@ input.cms-map__key { padding-top: 6px; }
 /* left panel: outline + blocks + nodes, one scroll (no tabs) */
 .cms-rail { pointer-events: auto; position: fixed; z-index: 2147483001; left: 12px; top: 12px; bottom: 76px; width: min(320px, calc(100vw - 24px)); display: flex; flex-direction: column; overflow: hidden; background: var(--cms-panel); border: 1px solid var(--cms-line); border-radius: 12px; box-shadow: 0 10px 40px rgba(0,0,0,.5); }
 .cms-rail > header { display: flex; align-items: center; justify-content: space-between; padding: 6px 6px 6px 12px; border-bottom: 1px solid var(--cms-line); font-weight: 600; }
+.cms-rail__resize { position: absolute; top: 0; bottom: 0; right: -5px; width: 12px; cursor: ew-resize; touch-action: none; z-index: 2; }
+.cms-rail__resize::after { content: ''; position: absolute; top: 10px; bottom: 10px; right: 5px; width: 2px; border-radius: 2px; background: transparent; }
+.cms-rail__resize:hover::after { background: var(--cms-accent); }
 .cms-rail__title { display: inline-flex; align-items: center; gap: 8px; }
 .cms-rail__body { overflow-y: auto; flex: 1; min-height: 0; padding-bottom: 12px; }
 .cms-rail__body > section + section { border-top: 1px solid var(--cms-line); margin-top: 8px; padding-top: 4px; }