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.

toolsets.py

@@ -38,7 +38,7 @@ _HERMES_CORE_TOOLS = [
     # Vision + image generation
     "vision_analyze", "image_generate",
     # Skills
-    "skills_list", "skill_view", "skill_manage",
+    "skills_list", "skill_view", "skill_manage", "skills_reload",
     # Browser automation
     "browser_navigate", "browser_snapshot", "browser_click",
     "browser_type", "browser_scroll", "browser_back",
@@ -105,7 +105,7 @@ TOOLSETS = {
     
     "skills": {
         "description": "Access, create, edit, and manage skill documents with specialized instructions and knowledge",
-        "tools": ["skills_list", "skill_view", "skill_manage"],
+        "tools": ["skills_list", "skill_view", "skill_manage", "skills_reload"],
         "includes": []
     },
     
@@ -279,7 +279,7 @@ TOOLSETS = {
             "terminal", "process",
             "read_file", "write_file", "patch", "search_files",
             "vision_analyze",
-            "skills_list", "skill_view", "skill_manage",
+            "skills_list", "skill_view", "skill_manage", "skills_reload",
             "browser_navigate", "browser_snapshot", "browser_click",
             "browser_type", "browser_scroll", "browser_back",
             "browser_press", "browser_get_images",
@@ -303,7 +303,7 @@ TOOLSETS = {
             # Vision + image generation
             "vision_analyze", "image_generate",
             # Skills
-            "skills_list", "skill_view", "skill_manage",
+            "skills_list", "skill_view", "skill_manage", "skills_reload",
             # Browser automation
             "browser_navigate", "browser_snapshot", "browser_click",
             "browser_type", "browser_scroll", "browser_back",