chore: housekeeping for v0.3 prep

- Pin KUBESOLO_VERSION in versions.env (was soft-defaulted in fetch-components.sh)
- Gitignore screenshots, macOS resource forks, and common image extensions
- Update README roadmap: x86_64 stable, ARM64 generic in progress (v0.3),
  ARM64 RPi paused pending hardware
- Add docs/ci-runners.md documenting the Odroid arm64-linux Gitea runner

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

build/scripts/fetch-components.sh

@@ -51,8 +51,7 @@ if [ "$FETCH_ARCH" = "arm64" ]; then
     echo "==> Fetching RPi firmware..."
     "$SCRIPT_DIR/fetch-rpi-firmware.sh"
 
-    # Download ARM64 KubeSolo binary
-    KUBESOLO_VERSION="${KUBESOLO_VERSION:-v1.1.0}"
+    # Download ARM64 KubeSolo binary (KUBESOLO_VERSION set from versions.env)
     KUBESOLO_BIN_ARM64="$CACHE_DIR/kubesolo-arm64"
     if [ -f "$KUBESOLO_BIN_ARM64" ]; then
         echo "==> KubeSolo ARM64 binary already cached: $KUBESOLO_BIN_ARM64"
@@ -112,7 +111,7 @@ else
 fi
 
 # --- KubeSolo ---
-KUBESOLO_VERSION="${KUBESOLO_VERSION:-v1.1.0}"
+# KUBESOLO_VERSION sourced from versions.env
 KUBESOLO_BIN="$CACHE_DIR/kubesolo"
 
 if [ -f "$KUBESOLO_BIN" ]; then