docs: update README, installation guide and GitHub Pages

- README: GHCR badge, Kanban quick-status buttons and configurable
  currency mentioned in highlights
- installation.md: Option A (pre-built image, no clone) as primary path,
  Option B (build from source) as alternative; Updates section updated;
  SQLCipher troubleshooting tip added
- index.html: Get Started block now shows pre-built image path;
  task and budget feature cards updated (EN + DE translations)

package.json

@@ -1,6 +1,6 @@
 {
   "name": "oikos",
-  "version": "0.11.8",
+  "version": "0.11.9",
   "description": "Self-hosted family planner - calendar, tasks, shopping, meal planning, budget and more. Private, open-source, no subscription.",
   "main": "server/index.js",
   "type": "module",