feat(ui): connection status in the header; README screenshots as WebP

- Desktop shows "offline" with a red dot under the user name when the
  server is unreachable; phones show a green/red dot on the avatar.
  Based on the app-wide realtime connection, so a server outage is
  noticed even while the device has network (4 s grace period).
- Screenshots converted to WebP (1280 px desktop, 480 px phone, q90),
  e2e/screenshots.sh converts with cwebp; new journal picture with
  round corners. Rules in AGENTS.md.
- Release v0.26.0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

e2e/screenshots.sh

@@ -1,6 +1,7 @@
 #!/usr/bin/env bash
 # Builds MindSift, starts it in demo mode with a fresh database and renews the README screenshots
 # in screenshots/ (title picture and colour-family grid: light and dark joined along a diagonal).
+# The PNGs from the browser are scaled down (desktop 1280 px, phone 480 px wide) and saved as WebP.
 # Requires podman (or docker via ENGINE=docker). Usage: e2e/screenshots.sh, other theme pair: SHOT_LIGHT=fjord SHOT_DARK=fjord-night
 set -euo pipefail
 ENGINE="${ENGINE:-podman}"
@@ -21,6 +22,7 @@ cleanup() {
   rm -rf "$WORK"
 }
 trap cleanup EXIT
+mkdir -p "$WORK/png"
 
 echo "Baue Image …"
 # Version in the header, e.g. APP_VERSION=v0.2 e2e/screenshots.sh
@@ -32,5 +34,14 @@ for _ in $(seq 1 60); do curl -s -m 1 "http://localhost:$PORT/api/v1/health" >/d
 echo "Erstelle Screenshots …"
 "$ENGINE" run --rm --network host -e MINDSIFT_URL="http://localhost:$PORT" -e SHOTS_DIR=/shots \
   -e SHOT_LIGHT="${SHOT_LIGHT:-light}" -e SHOT_DARK="${SHOT_DARK:-dark}" -e LANG=de_DE.UTF-8 -e TZ=Europe/Berlin \
-  -v "$ROOT/e2e":/e2e:Z -v "$ROOT/screenshots":/shots:Z -w /e2e mcr.microsoft.com/playwright:v1.48.2-jammy \
+  -v "$ROOT/e2e":/e2e:Z -v "$WORK/png":/shots:Z -w /e2e mcr.microsoft.com/playwright:v1.48.2-jammy \
   sh -c 'npm install --no-audit --no-fund >/dev/null 2>&1 && node screenshots.mjs'
+
+echo "Wandle in WebP um …"
+"$ENGINE" run --rm -v "$WORK/png":/png:Z -v "$ROOT/screenshots":/shots:Z docker.io/library/alpine:3.20 sh -c '
+  apk add -q libwebp-tools >/dev/null
+  for f in /png/*.png; do
+    name=$(basename "$f" .png)
+    case "$name" in Mobile_*) width=480 ;; *) width=1280 ;; esac
+    cwebp -quiet -resize "$width" 0 -q 90 -m 6 -metadata none "$f" -o "/shots/$name.webp"
+  done'