feat(skills): /reload-skills slash command + skills_reload agent tool

Adds a public reload path for the in-process skill caches so newly
installed (or removed) skills become visible mid-session without a
gateway restart. Mirrors the shape of /reload-mcp.

Three surfaces:
* /reload-skills slash command — CLI (cli.py) and gateway (gateway/run.py),
  with /reload_skills alias for Telegram autocomplete and an explicit
  Discord registration.
* skills_reload agent tool (tools/skills_tool.py) — lets agents/subagents
  pick up freshly-installed skills via tool call.
* agent.skill_commands.reload_skills() — shared helper that clears
  _skill_commands, _SKILLS_PROMPT_CACHE (in-process LRU), and the
  on-disk .skills_prompt_snapshot.json, then returns an added/removed
  diff plus the new total count.

Tested:
* tests/agent/test_skill_commands_reload.py (9 cases)
* tests/cli/test_cli_reload_skills.py       (3 cases)
* tests/gateway/test_reload_skills_command.py (4 cases)

Use case: NemoClaw / OpenShell-style sandboxed orchestrators that drop
skills into ~/.hermes/skills mid-session, plus agentic flows where the
agent itself installs a skill via the shell tool and needs it bound
without a gateway restart. The Python helper
clear_skills_system_prompt_cache(clear_snapshot=True) already exists
internally — this PR just exposes it via slash command and tool.

tools/skills_tool.py

@@ -1512,3 +1512,61 @@ registry.register(
     check_fn=check_skills_requirements,
     emoji="📚",
 )
+
+
+# ---------------------------------------------------------------------------
+# skills_reload — rescan the skills dir without restarting the gateway
+# ---------------------------------------------------------------------------
+
+def skills_reload(task_id: str | None = None) -> str:
+    """Re-scan ``~/.hermes/skills/`` and clear in-process skill caches.
+
+    Use this after installing a skill via the shell during a session so the
+    new skill becomes visible to ``skills_list`` / ``skill_view`` and the
+    skill catalogue in the system prompt without a gateway restart.
+
+    Returns:
+        JSON string with ``added``, ``removed``, ``unchanged``, ``total``,
+        and ``commands`` keys. ``added``/``removed`` are bare skill names
+        (no leading slash).
+    """
+    try:
+        from agent.skill_commands import reload_skills as _reload
+        result = _reload()
+    except Exception as e:
+        return json.dumps({"success": False, "error": str(e)})
+
+    return json.dumps({
+        "success": True,
+        "added": result.get("added", []),
+        "removed": result.get("removed", []),
+        "unchanged_count": len(result.get("unchanged", [])),
+        "total": result.get("total", 0),
+        "commands": result.get("commands", 0),
+    })
+
+
+SKILLS_RELOAD_SCHEMA = {
+    "name": "skills_reload",
+    "description": (
+        "Re-scan the skills directory and clear in-process skill caches. "
+        "Use after installing or removing a skill mid-session (e.g. via the "
+        "shell tool or skills_hub) so the new skill becomes visible to "
+        "skills_list / skill_view without restarting the gateway. Returns "
+        "the diff of added/removed skill names plus the new total count."
+    ),
+    "parameters": {
+        "type": "object",
+        "properties": {},
+        "required": [],
+    },
+}
+
+registry.register(
+    name="skills_reload",
+    toolset="skills",
+    schema=SKILLS_RELOAD_SCHEMA,
+    handler=lambda args, **kw: skills_reload(task_id=kw.get("task_id")),
+    check_fn=check_skills_requirements,
+    emoji="🔄",
+)