Eliminate duplicate wiki-tool implementations in skill/tools.py

[wutongyuonce]

Problem

openkb/skill/tools.py claims to "wrap the canonical wiki tools" from
openkb/agent/tools.py, but two of its five functions were independent
re-implementations rather than wrappers:

skill/tools.py function	agent/tools.py equivalent	Status before this PR
list_wiki_dir	list_wiki_files	Duplicate (identical logic, different variable names)
read_wiki_file_for_skill	read_wiki_file	Duplicate (identical logic, different variable names)
get_skill_page_content	get_wiki_page_content	Already delegates
read_skill_image	read_wiki_image	Already delegates
write_skill_file	(no equivalent — genuinely different)	Own implementation (correct)

This creates two risks:

1. Divergence — a bug fix or behavior change applied to one copy can be
   forgotten in the other, creating a "two sources of truth" problem.
2. False confidence — the module docstring promises "no second
   implementation to drift" while the code contradicts it.

Solution

Replace the bodies of list_wiki_dir and read_wiki_file_for_skill with
single-line delegations to their canonical counterparts in
openkb/agent/tools.py, matching the pattern already established by
get_skill_page_content and read_skill_image.

Changes

1 file changed: openkb/skill/tools.py

• Imports: added list_wiki_files as _list_wiki_files and
  read_wiki_file as _read_wiki_file from openkb.agent.tools.
• list_wiki_dir: body replaced with return _list_wiki_files(directory, wiki_root).
• read_wiki_file_for_skill: body replaced with return _read_wiki_file(path, wiki_root).
• Module docstring: updated to accurately reflect that all four READ
  functions are now delegated.
• write_skill_file: unchanged (genuinely different security boundary).