feat: system service management (gyandoot service install|remove|status)

- Create systemd + launchd service templates in resources/
- Add gyandoot-core/src/service.rs module with full lifecycle
  - systemd: user service, daemon-reload, enable, start, stop, disable
  - launchd: macOS plist, load/unload, start/stop (launchctl)
- Add 'gyandoot service install|remove|status' CLI subcommand
- Update setup wizard: prompts 'Install system service? [y/N]'
- Update install.sh: prompts user for service install after binary
- Browser auto-starts at runtime (browser_manager), no separate service needed
- Camoufox installed via npm, auto-started by GyanDoot agent loop

resources/launchd/com.gyandoot.agent.plist

@@ -0,0 +1,52 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+    <key>Label</key>
+    <string>com.gyandoot.agent</string>
+
+    <key>ProgramArguments</key>
+    <array>
+        <string>%BINARY%</string>
+        <string>serve</string>
+        <string>--host</string>
+        <string>127.0.0.1</string>
+        <string>--port</string>
+        <string>8777</string>
+    </array>
+
+    <key>RunAtLoad</key>
+    <true/>
+
+    <key>KeepAlive</key>
+    <dict>
+        <key>SuccessfulExit</key>
+        <false/>
+        <key>Crashed</key>
+        <true/>
+    </dict>
+
+    <key>WatchPaths</key>
+    <array>
+        <string>%HOME%/.config/gyandoot/config.toml</string>
+    </array>
+
+    <key>StandardOutPath</key>
+    <string>%HOME%/.gyandoot/service.log</string>
+    <key>StandardErrorPath</key>
+    <string>%HOME%/.gyandoot/service.log</string>
+
+    <key>EnvironmentVariables</key>
+    <dict>
+        <key>GYANDOOT_CONFIG</key>
+        <string>%HOME%/.config/gyandoot/config.toml</string>
+        <key>GYANDOOT_LOG</key>
+        <string>info</string>
+        <key>PATH</key>
+        <string>/usr/local/bin:/usr/bin:/bin:%HOME%/.local/bin</string>
+    </dict>
+
+    <key>WorkingDirectory</key>
+    <string>%HOME%/.gyandoot</string>
+</dict>
+</plist>