feat: edit in the Changes panel, git graph history, plan quota (v2.3.0)

- Changes panel: a working file opens in a CodeMirror editor with its diff
  inline (DiffEditor.tsx, @codemirror/merge, lazy-loaded); Changes folds the
  unchanged lines, Whole file shows them; side by side at 50/50 and full
  width; a Revert per block; original from HEAD or the branch's merge base
  (`mergeBase` on GET /git/changes?range=branch)
- Every diff: green = line added whole, red = removed whole, blue = edited
  in place (--diff-mod)
- History drawn as a commit graph (#58: `parents` on GET /git/log,
  --date-order; lib/commitGraph.ts)
- Per-workspace never-stage list, drawn orange in the Files tree (--kept);
  closed Terminal rows past three deleted
- Status bar plan quota for Claude (per account) and Codex
  (GET /api/pricing/quota, server/lib/quota.js); compact hover panel that
  stays open, Refresh button with a spinner
- Settings → Appearance holds language, theme and pet; Ctrl+Shift+C copies;
  compact sidebar navigation and short session times

client/src/i18n/locales/en/settings.json

@@ -21,7 +21,7 @@
       "import": "Import .codex-pet bundle…",
       "browse": "Find more on codex-pets.net",
       "settings": "Pet settings…",
-      "hiddenToast": "Pet hidden. Show it again in Settings → Pet.",
+      "hiddenToast": "Pet hidden. Show it again in Settings → Appearance.",
       "deleteTitle": "Delete {{name}}?",
       "deleteMessage": "The pet's files are removed from this install. A featured pet can be downloaded again; an upload is gone for good.",
       "deleteConfirm": "Delete pet",
@@ -653,7 +653,10 @@
     "reset": "Reset to defaults",
     "resetTitle": "Reset appearance?",
     "resetBody": "Mode goes back to Dark and both modes to their default theme.",
-    "resetDone": "Appearance reset."
+    "resetDone": "Appearance reset.",
+    "theme": "Theme",
+    "pet": "Pet",
+    "petDescription": "The corner mascot: show it, its size, speech bubbles, and which pet it wears."
   },
   "gitCreds": {
     "title": "Git credentials",
@@ -753,17 +756,9 @@
       "cost": "Cost"
     },
     "section": {
-      "general": {
-        "title": "General",
-        "description": "The dashboard's display language."
-      },
       "appearance": {
         "title": "Appearance",
-        "description": "Colour mode and theme. Saved in this browser only."
-      },
-      "pet": {
-        "title": "Pet",
-        "description": "The corner mascot: show it, its size, speech bubbles, and which pet it wears."
+        "description": "Language, colour mode and theme, and the corner pet."
       },
       "notifications": {
         "title": "Notifications",