Refresh README, add CONTRIBUTING guide, harden CI

- README: modernize visual layout (status badges row, tagline,
  Ko-fi shields badge, expanded Contributing section). Update
  web URLs to proxmenux.com/en for the new locale-prefixed site.
- CONTRIBUTING.md: add as the canonical contributor guide. Fix
  the workflow section to branch from develop (not main), add
  a dedicated "dialog vs whiptail" section, reorder so Script
  Header comes first.
- deploy.yml: switch npm install -> npm ci so the build uses
  the committed lockfile; fix cache-dependency-path to track
  web/package-lock.json (was package.json); add scripts/** to
  the path triggers so script edits redeploy the doc site.
- .gitignore: ignore the accidental root-level package.json /
  package-lock.json (pagefind is declared in web/package.json)
  and the regenerated build artifacts web/public/pagefind/ and
  web/public/scripts/.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.github/workflows/deploy.yml

@@ -7,6 +7,7 @@ on:
     paths:
       - "web/**"
       - "guides/**"
+      - "scripts/**"
       - "CHANGELOG.md"
   workflow_dispatch:
 
@@ -31,15 +32,15 @@ jobs:
         with:
           node-version: "20"
           cache: 'npm'
-          cache-dependency-path: 'web/package.json'
+          cache-dependency-path: 'web/package-lock.json'
 
       - name: Setup Pages
         uses: actions/configure-pages@v4
 
-      - name: Install dependencies and generate lock file
+      - name: Install dependencies
         run: |
           cd web
-          npm install
+          npm ci
 
       - name: Build with Next.js
         run: |