feat(security): add tirith pre-exec command scanning

Integrate tirith as a pre-execution security scanner that detects
homograph URLs, pipe-to-interpreter patterns, terminal injection,
zero-width Unicode, and environment variable manipulation — threats
the existing 50-pattern dangerous command detector doesn't cover.

Architecture: gather-then-decide — both tirith and the dangerous
command detector run before any approval prompt, preventing gateway
force=True replay from bypassing one check when only the other was
shown to the user.

New files:
- tools/tirith_security.py: subprocess wrapper with auto-installer,
  mandatory cosign provenance verification, non-blocking background
  download, disk-persistent failure markers with retryable-cause
  tracking (cosign_missing auto-clears when cosign appears on PATH)
- tests/tools/test_tirith_security.py: 62 tests covering exit code
  mapping, fail_open, cosign verification, background install,
  HERMES_HOME isolation, and failure recovery
- tests/tools/test_command_guards.py: 21 integration tests for the
  combined guard orchestration

Modified files:
- tools/approval.py: add check_all_command_guards() orchestrator,
  add allow_permanent parameter to prompt_dangerous_approval()
- tools/terminal_tool.py: replace _check_dangerous_command with
  consolidated check_all_command_guards
- cli.py: update _approval_callback for allow_permanent kwarg,
  call ensure_installed() at startup
- gateway/run.py: iterate pattern_keys list on replay approval,
  call ensure_installed() at startup
- hermes_cli/config.py: add security config defaults, split
  commented sections for independent fallback
- cli-config.yaml.example: document tirith security config

cli-config.yaml.example

@@ -178,6 +178,20 @@ terminal:
 # Example (add to your terminal section):
 #   sudo_password: "your-password-here"
 
+# =============================================================================
+# Security Scanning (tirith)
+# =============================================================================
+# Optional pre-exec command security scanning via tirith.
+# Detects homograph URLs, pipe-to-shell, terminal injection, env manipulation.
+# Install: brew install sheeki03/tap/tirith
+# Docs: https://github.com/sheeki03/tirith
+#
+# security:
+#   tirith_enabled: true        # Enable/disable tirith scanning
+#   tirith_path: "tirith"       # Path to tirith binary (supports ~ expansion)
+#   tirith_timeout: 5           # Scan timeout in seconds
+#   tirith_fail_open: true      # Allow commands if tirith unavailable
+
 # =============================================================================
 # Browser Tool Configuration
 # =============================================================================