refactor(commands): drop /provider, /plan handler, and clean up slash registry (#15047)

* refactor(commands): drop /provider and clean up slash registry

* refactor(commands): drop /plan special handler — use plain skill dispatch

tests/agent/test_skill_commands.py

@@ -1,13 +1,11 @@
 """Tests for agent/skill_commands.py — skill slash command scanning and platform filtering."""
 
 import os
-from datetime import datetime
 from pathlib import Path
 from unittest.mock import patch
 
 import tools.skills_tool as skills_tool_module
 from agent.skill_commands import (
-    build_plan_path,
     build_preloaded_skills_prompt,
     build_skill_invocation_message,
     resolve_skill_command_key,
@@ -399,40 +397,6 @@ Generate some audio.
         assert 'file_path="<path>"' in msg
 
 
-class TestPlanSkillHelpers:
-    def test_build_plan_path_uses_workspace_relative_dir_and_slugifies_request(self):
-        path = build_plan_path(
-            "Implement OAuth login + refresh tokens!",
-            now=datetime(2026, 3, 15, 9, 30, 45),
-        )
-
-        assert path == Path(".hermes") / "plans" / "2026-03-15_093045-implement-oauth-login-refresh-tokens.md"
-
-    def test_plan_skill_message_can_include_runtime_save_path_note(self, tmp_path):
-        with patch("tools.skills_tool.SKILLS_DIR", tmp_path):
-            _make_skill(
-                tmp_path,
-                "plan",
-                body="Save plans under .hermes/plans in the active workspace and do not execute the work.",
-            )
-            scan_skill_commands()
-            msg = build_skill_invocation_message(
-                "/plan",
-                "Add a /plan command",
-                runtime_note=(
-                    "Save the markdown plan with write_file to this exact relative path inside "
-                    "the active workspace/backend cwd: .hermes/plans/plan.md"
-                ),
-            )
-
-        assert msg is not None
-        assert "Save plans under $HERMES_HOME/plans" not in msg
-        assert ".hermes/plans" in msg
-        assert "Add a /plan command" in msg
-        assert ".hermes/plans/plan.md" in msg
-        assert "Runtime note:" in msg
-
-
 class TestSkillDirectoryHeader:
     """The activation message must expose the absolute skill directory and
     explain how to resolve relative paths, so skills with bundled scripts