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>

.gitignore

@@ -6,6 +6,14 @@ web/out/
 web/node_modules/
 node_modules/
 
+# Local-only — accidental pagefind install at project root.
+# Pagefind is declared and installed from web/package.json; the
+# CI build (.github/workflows/deploy.yml) only runs
+# `cd web && npm install`, so a root-level package.json/lock is
+# never consumed and just adds noise. Keep them ignored.
+/package.json
+/package-lock.json
+
 # Logs
 web/*.log
 *.log
@@ -33,6 +41,15 @@ Thumbs.db
 /web/.next
 /web/out
 
+# Build artifacts generated by web's prebuild + build scripts.
+# `prebuild` runs `sync:scripts` which rsyncs ../scripts/ into
+# public/scripts/. `build` runs pagefind --site out which writes the
+# search index into public/pagefind/. Both are regenerated fresh by
+# the GitHub Pages CI on every deploy; committing them would just
+# bloat the repo and produce constant noise in `git status`.
+/web/public/pagefind/
+/web/public/scripts/
+
 # Cache
 .cache
 /web/.cache