fix(security): harden terminal safety and sandbox file writes (#1653)

* fix(security): harden terminal safety and sandbox file writes

Two security improvements:

1. Dangerous command detection: expand shell -c pattern to catch
   combined flags (bash -lc, bash -ic, ksh -c) that were previously
   undetected. Pattern changed from matching only 'bash -c' to
   matching any shell invocation with -c anywhere in the flags.

2. File write sandboxing: add HERMES_WRITE_SAFE_ROOT env var that
   constrains all write_file/patch operations to a configured directory
   tree. Opt-in — when unset, behavior is unchanged. Useful for
   gateway/messaging deployments that should only touch a workspace.

Based on PR #1085 by ismoilh.

* fix: correct "POSIDEON" typo to "POSEIDON" in banner ASCII art

The poseidon skin's banner_logo had the E and I letters swapped,
spelling "POSIDEON-AGENT" instead of "POSEIDON-AGENT".

---------

Co-authored-by: ismoilh <ismoilh@users.noreply.github.com>
Co-authored-by: unmodeled-tyler <unmodeled.tyler@proton.me>

hermes_cli/skin_engine.py

@@ -351,12 +351,12 @@ _BUILTIN_SKINS: Dict[str, Dict[str, Any]] = {
             "help_header": "(Ψ) Available Commands",
         },
         "tool_prefix": "│",
-        "banner_logo": """[bold #B8E8FF]██████╗  ██████╗ ███████╗██╗██████╗ ███████╗ ██████╗ ███╗   ██╗       █████╗  ██████╗ ███████╗███╗   ██╗████████╗[/]
-[bold #97D6FF]██╔══██╗██╔═══██╗██╔════╝██║██╔══██╗██╔════╝██╔═══██╗████╗  ██║      ██╔══██╗██╔════╝ ██╔════╝████╗  ██║╚══██╔══╝[/]
-[#75C1F6]██████╔╝██║   ██║███████╗██║██║  ██║█████╗  ██║   ██║██╔██╗ ██║█████╗███████║██║  ███╗█████╗  ██╔██╗ ██║   ██║[/]
-[#4FA2E0]██╔═══╝ ██║   ██║╚════██║██║██║  ██║██╔══╝  ██║   ██║██║╚██╗██║╚════╝██╔══██║██║   ██║██╔══╝  ██║╚██╗██║   ██║[/]
-[#2E7CC7]██║     ╚██████╔╝███████║██║██████╔╝███████╗╚██████╔╝██║ ╚████║      ██║  ██║╚██████╔╝███████╗██║ ╚████║   ██║[/]
-[#1B4F95]╚═╝      ╚═════╝ ╚══════╝╚═╝╚═════╝ ╚══════╝ ╚═════╝ ╚═╝  ╚═══╝      ╚═╝  ╚═╝ ╚═════╝ ╚══════╝╚═╝  ╚═══╝   ╚═╝[/]""",
+        "banner_logo": """[bold #B8E8FF]██████╗  ██████╗ ███████╗███████╗██╗██████╗  ██████╗ ███╗   ██╗       █████╗  ██████╗ ███████╗███╗   ██╗████████╗[/]
+[bold #97D6FF]██╔══██╗██╔═══██╗██╔════╝██╔════╝██║██╔══██╗██╔═══██╗████╗  ██║      ██╔══██╗██╔════╝ ██╔════╝████╗  ██║╚══██╔══╝[/]
+[#75C1F6]██████╔╝██║   ██║███████╗█████╗  ██║██║  ██║██║   ██║██╔██╗ ██║█████╗███████║██║  ███╗█████╗  ██╔██╗ ██║   ██║[/]
+[#4FA2E0]██╔═══╝ ██║   ██║╚════██║██╔══╝  ██║██║  ██║██║   ██║██║╚██╗██║╚════╝██╔══██║██║   ██║██╔══╝  ██║╚██╗██║   ██║[/]
+[#2E7CC7]██║     ╚██████╔╝███████║███████╗██║██████╔╝╚██████╔╝██║ ╚████║      ██║  ██║╚██████╔╝███████╗██║ ╚████║   ██║[/]
+[#1B4F95]╚═╝      ╚═════╝ ╚══════╝╚══════╝╚═╝╚═════╝  ╚═════╝ ╚═╝  ╚═══╝      ╚═╝  ╚═╝ ╚═════╝ ╚══════╝╚═╝  ╚═══╝   ╚═╝[/]""",
         "banner_hero": """[#2A6FB9]⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣀⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀[/]
 [#5DB8F5]⠀⠀⠀⠀⠀⠀⠀⠀⠀⣠⣾⣿⣷⣄⠀⠀⠀⠀⠀⠀⠀⠀⠀[/]
 [#5DB8F5]⠀⠀⠀⠀⠀⠀⠀⢠⣿⠏⠀Ψ⠀⠹⣿⡄⠀⠀⠀⠀⠀⠀⠀[/]