fix: disabled skills respected across banner, system prompt, slash commands, and skill_view (#1897)

* fix: banner skill count now respects disabled skills and platform filtering

The banner's get_available_skills() was doing a raw rglob scan of
~/.hermes/skills/ without checking:
- Whether skills are disabled (skills.disabled config)
- Whether skills match the current platform (platforms: frontmatter)

This caused the banner to show inflated skill counts (e.g. '100 skills'
when many are disabled) and list macOS-only skills on Linux.

Fix: delegate to _find_all_skills() from tools/skills_tool which already
handles both platform gating and disabled-skill filtering.

* fix: system prompt and slash commands now respect disabled skills

Two more places where disabled skills were still surfaced:

1. build_skills_system_prompt() in prompt_builder.py — disabled skills
   appeared in the <available_skills> system prompt section, causing
   the agent to suggest/load them despite being disabled.

2. scan_skill_commands() in skill_commands.py — disabled skills still
   registered as /skill-name slash commands in CLI help and could be
   invoked.

Both now load _get_disabled_skill_names() and filter accordingly.

* fix: skill_view blocks disabled skills

skill_view() checked platform compatibility but not disabled state,
so the agent could still load and read disabled skills directly.

Now returns a clear error when a disabled skill is requested, telling
the user to enable it via hermes skills or inspect the files manually.

---------

Co-authored-by: Test <test@test.com>

agent/skill_commands.py

@@ -157,9 +157,10 @@ def scan_skill_commands() -> Dict[str, Dict[str, Any]]:
     global _skill_commands
     _skill_commands = {}
     try:
-        from tools.skills_tool import SKILLS_DIR, _parse_frontmatter, skill_matches_platform
+        from tools.skills_tool import SKILLS_DIR, _parse_frontmatter, skill_matches_platform, _get_disabled_skill_names
         if not SKILLS_DIR.exists():
             return _skill_commands
+        disabled = _get_disabled_skill_names()
         for skill_md in SKILLS_DIR.rglob("SKILL.md"):
             if any(part in ('.git', '.github', '.hub') for part in skill_md.parts):
                 continue
@@ -170,6 +171,9 @@ def scan_skill_commands() -> Dict[str, Dict[str, Any]]:
                 if not skill_matches_platform(frontmatter):
                     continue
                 name = frontmatter.get('name', skill_md.parent.name)
+                # Respect user's disabled skills config
+                if name in disabled:
+                    continue
                 description = frontmatter.get('description', '')
                 if not description:
                     for line in body.strip().split('\n'):