Add Skills Hub — universal skill search, install, and management from online registries

Implements the Hermes Skills Hub with agentskills.io spec compliance,
multi-registry skill discovery, security scanning, and user-driven
management via CLI and /skills slash command.

Core features:
- Security scanner (tools/skills_guard.py): 120 threat patterns across
  12 categories, trust-aware install policy (builtin/trusted/community),
  structural checks, unicode injection detection, LLM audit pass
- Hub client (tools/skills_hub.py): GitHub, ClawHub, Claude Code
  marketplace, and LobeHub source adapters with shared GitHubAuth
  (PAT + gh CLI + GitHub App), lock file provenance tracking, quarantine
  flow, and unified search across all sources
- CLI interface (hermes_cli/skills_hub.py): search, install, inspect,
  list, audit, uninstall, publish (GitHub PR), snapshot export/import,
  and tap management — powers both `hermes skills` and `/skills`

Spec conformance (Phase 0):
- Upgraded frontmatter parser to yaml.safe_load with fallback
- Migrated 39 SKILL.md files: tags/related_skills to metadata.hermes.*
- Added assets/ directory support and compatibility/metadata fields
- Excluded .hub/ from skill discovery in skills_tool.py

Updated 13 config/doc files including README, AGENTS.md, .env.example,
setup wizard, doctor, status, pyproject.toml, and docs.

cli.py

@@ -549,6 +549,7 @@ COMMANDS = {
     "/save": "Save the current conversation",
     "/config": "Show current configuration",
     "/cron": "Manage scheduled tasks (list, add, remove)",
+    "/skills": "Search, install, inspect, or manage skills from online registries",
     "/platforms": "Show gateway/messaging platform status",
     "/quit": "Exit the CLI (also: /exit, /q)",
 }
@@ -1276,6 +1277,11 @@ class HermesCLI:
             print(f"(._.) Unknown cron command: {subcommand}")
             print("  Available: list, add, remove")
     
+    def _handle_skills_command(self, cmd: str):
+        """Handle /skills slash command — delegates to hermes_cli.skills_hub."""
+        from hermes_cli.skills_hub import handle_skills_slash
+        handle_skills_slash(cmd, self.console)
+
     def _show_gateway_status(self):
         """Show status of the gateway and connected messaging platforms."""
         from gateway.config import load_gateway_config, Platform
@@ -1401,6 +1407,8 @@ class HermesCLI:
             self.save_conversation()
         elif cmd_lower.startswith("/cron"):
             self._handle_cron_command(cmd_original)
+        elif cmd_lower.startswith("/skills"):
+            self._handle_skills_command(cmd_original)
         elif cmd_lower == "/platforms" or cmd_lower == "/gateway":
             self._show_gateway_status()
         else: