feat(extras): add silent-send module + new extras category

Adds services/silent-send.sh — installs the Silent Send browser extension
(client-side PII redaction for AI chat). Non-docker module: installs git +
Node.js >=18 (NodeSource) + npm, clones outis1one/silent-send to ~/silent-send,
runs npm install (readies web-ext for Firefox build/sign), optionally builds a
signed Firefox .xpi, and prints per-browser load/build instructions. README
written to the checkout.

Introduces a new 'extras' category for non-docker add-ons pulled from other
repos, wired into setup.sh CATEGORY_ORDER (gaming -> extras -> backup) with an
is_installed marker. MODULAR.md groups list updated.

Bumps version to 0.9.9.

setup.sh

@@ -20,7 +20,7 @@ set -uo pipefail
 HERE="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 
 # Category display order (groups not listed here are appended alphabetically).
-CATEGORY_ORDER=(base homelab utilities media cameras gaming backup)
+CATEGORY_ORDER=(base homelab utilities media cameras gaming extras backup)
 # Service ordering hint within a category (lower = earlier). Default 50.
 declare -A SERVICE_PRIORITY=( [caddy]=1 [crowdsec]=2 [authelia]=3 )
 
@@ -79,6 +79,7 @@ is_installed() {
         base) command -v ncdu >/dev/null 2>&1 ;;
         glow) command -v glow >/dev/null 2>&1 ;;
         crowdsec) command -v cscli >/dev/null 2>&1 ;;
+        silent-send) [ -d "$ACTUAL_HOME/silent-send/.git" ] ;;
         *) [ -e "$DOCKER_DIR/$1" ] ;;
     esac
 }