refactor(agent): streamline hook method calls and enhance error logging

- Introduced a helper method `_for_each_hook_safe` to reduce code duplication in hook method implementations.
- Updated error logging to include the method name for better traceability.
- Improved the `SkillsLoader` class by adding a new method `_skill_entries_from_dir` to simplify skill listing logic.
- Enhanced skill loading and filtering logic, ensuring workspace skills take precedence over built-in ones.
- Added comprehensive tests for `SkillsLoader` to validate functionality and edge cases.

tests/tools/test_tool_validation.py

@@ -1,3 +1,6 @@
+import shlex
+import subprocess
+import sys
 from typing import Any
 
 from nanobot.agent.tools import (
@@ -546,10 +549,15 @@ async def test_exec_head_tail_truncation() -> None:
     """Long output should preserve both head and tail."""
     tool = ExecTool()
     # Generate output that exceeds _MAX_OUTPUT (10_000 chars)
-    # Use python to generate output to avoid command line length limits
-    result = await tool.execute(
-        command="python -c \"print('A' * 6000 + '\\n' + 'B' * 6000)\""
-    )
+    # Use current interpreter (PATH may not have `python`). ExecTool uses
+    # create_subprocess_shell: POSIX needs shlex.quote; Windows uses cmd.exe
+    # rules, so list2cmdline is appropriate there.
+    script = "print('A' * 6000 + '\\n' + 'B' * 6000)"
+    if sys.platform == "win32":
+        command = subprocess.list2cmdline([sys.executable, "-c", script])
+    else:
+        command = f"{shlex.quote(sys.executable)} -c {shlex.quote(script)}"
+    result = await tool.execute(command=command)
     assert "chars truncated" in result
     # Head portion should start with As
     assert result.startswith("A")