feat: add feature-flag subsystem with on-demand features install

- Move autostart.sh from bin/ to features/ so re-installs never reset it
- Add lib/flags.sh (flag_set/clear/is_set/value/list/status) + flag-reader/set/clear CLIs
- install.sh --feature copies features/* to /usr/local/bin with overwrite prompt, sets flags
- postinstall.sh enables autostart.service only when the autostart flag is set
- Document features & flags in README, DEV.md, AGENT_Context_Project.md

features/autostart.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+LOG="${HOME:-/root}/.autostart.log"
+
+echo "[$(date)] autostart running" >> "$LOG" 2>/dev/null || true
+
+# Check network connectivity
+if ping -c 1 -W 2 8.8.8.8 &>/dev/null; then
+    echo "[$(date)] Network: online" >> "$LOG" 2>/dev/null || true
+else
+    echo "[$(date)] Network: offline" >> "$LOG" 2>/dev/null || true
+fi
+
+echo "[$(date)] autostart complete" >> "$LOG" 2>/dev/null || true