add security hardening features (#543)

* add security hardening features

- Add authentication vault (`auth save/login/list/show/delete`) so credentials are stored locally and never exposed to the LLM (fixes Snyk W007)
- Add `--content-boundaries` flag to wrap page-sourced output in structural markers, helping LLMs distinguish tool output from untrusted page content (fixes Snyk W011)
- Add `--allowed-domains` flag to restrict browser navigation to trusted domains
- Add `--action-policy` for static allow/deny gating of action categories, with opt-in `--confirm-actions`/`--confirm-interactive` for orchestrator or human-in-the-loop confirmation
- Add `--max-output` flag to truncate large page outputs, preventing context flooding
- New docs page at /security, updated README, SKILL.md, CLI help text, and templates

* fixes

* fixes

* fixes

* fixes

* fixes

* fixes

* fixes

* docs

skills/agent-browser/templates/authenticated-session.sh

@@ -3,6 +3,11 @@
 # Purpose: Login once, save state, reuse for subsequent runs
 # Usage: ./authenticated-session.sh <login-url> [state-file]
 #
+# RECOMMENDED: Use the auth vault instead of this template:
+#   echo "<pass>" | agent-browser auth save myapp --url <login-url> --username <user> --password-stdin
+#   agent-browser auth login myapp
+# The auth vault stores credentials securely and the LLM never sees passwords.
+#
 # Environment variables:
 #   APP_USERNAME - Login username/email
 #   APP_PASSWORD - Login password