feat(landing): add strict ESLint + Prettier with pre-commit hooks (#50)

- Install ESLint 9 with flat config, TypeScript, Vue plugins
- Configure Prettier (140 char, 2-space indent, single quotes)
- Add pre-commit hooks via husky + lint-staged for auto-fix
- Rename components to multi-word (Countdown → CountdownTimer, etc.)
- Add explicit TypeScript prop/emit interfaces
- Remove all console.log statements
- Fix all ESLint violations and type errors
- Verify type-check, build, and HMR working

resolves #43

Co-authored-by: johba <johba@harb.eth>
Reviewed-on: https://codeberg.org/johba/harb/pulls/50

landing/.lintstagedrc.json

@@ -0,0 +1,9 @@
+{
+  "src/**/*.{vue,ts}": [
+    "eslint --fix",
+    "prettier --write"
+  ],
+  "src/**/*.scss": [
+    "prettier --write"
+  ]
+}