fix(a11y): skip-link target, priority labels, greeting tokens

- Rename #page-content to #main-content so skip-to-content link
  targets the semantic <main> landmark
- Add sr-only priority labels to dashboard task items for screen
  readers (WCAG 1.4.1 color-not-only)
- Replace hardcoded hex in greeting gradient with accent tokens
  so dark mode themes the banner correctly
- Replace hardcoded gap: 2px with --space-0h token
- Bump version to 0.7.2

package.json

@@ -1,6 +1,6 @@
 {
   "name": "oikos",
-  "version": "0.7.1",
+  "version": "0.7.2",
   "description": "Self-hosted family planner - calendar, tasks, shopping, meal planning, budget and more. Private, open-source, no subscription.",
   "main": "server/index.js",
   "type": "module",