chore(release): v2.0.0 — full MUI frontend, zero custom CSS

Major release. The admin frontend is now entirely on Material UI v7:
every page and shared component migrated off ~7,100 lines of hand-written
CSS, and all five custom stylesheets (base/variables/plan/attendance/
offers) eliminated — global styles live in a theme-aware MUI <GlobalStyles>,
widgets (Quill, Leaflet, planner grid) in scoped styled() wrappers, and the
only remaining CSS imports are the two third-party libraries.

Also includes the post-migration polish: consistent page-entrance motion,
unified filters, mobile card layouts, readable status row tints, white-glyph
icon badges, single-key theme persistence, and the offer-page fixes
(heartbeat 401 handling, expires_in token lifetime, duplicate-key + motion
deprecation).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "app-ts",
-  "version": "1.9.8",
+  "version": "2.0.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "app-ts",
-      "version": "1.9.8",
+      "version": "2.0.0",
       "license": "ISC",
       "dependencies": {
         "@dnd-kit/core": "^6.3.1",