fix(check_framework_version): decode git diff output as UTF-8 (#511)

* fix(check_framework_version): decode git diff output as UTF-8

run_git() passed subprocess.run(text=True) with no explicit encoding,
so it fell back to the host locale's default codec - cp1252 on
Windows - instead of UTF-8. Any non-ASCII byte in a modified
framework file's diff (e.g. an em dash in a profile edit) then raised
UnicodeDecodeError before the gate could evaluate the change, instead
of a pass/fail verdict. Reproduced on a real Windows checkout.

Pin encoding="utf-8" on the subprocess.run() call. Added a regression
test that patches subprocess.run and asserts run_git() always passes
encoding="utf-8" - confirmed it fails against the pre-fix code and
passes against the fix.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* fix(check_framework_version): address review on UTF-8 decode fix

Per MadsLorentzen's review on PR #511:
- Add errors="replace" alongside encoding="utf-8" on the subprocess.run()
  call, matching the convention used elsewhere in this repo (robots_check.py).
- Correct the docstring: an em dash does not crash the un-pinned decode
  (cp1252 maps it fine); the actual trigger is a byte cp1252 leaves
  undefined, e.g. Cyrillic Ё/ё, much CJK, or Á-class Latin.
- Correct "profile file" to "framework file" - the tool only diffs the
  framework's own directories, not arbitrary profile files.
- Add a CHANGELOG entry under [Unreleased] / Fixed naming the tool and test.

---------

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

tools/check_framework_version.py

@@ -23,7 +23,14 @@ if root_agents.exists():
     FRAMEWORK_FILES.append(root_agents)
 
 def run_git(args: list[str]) -> tuple[int, str, str]:
-    res = subprocess.run(["git"] + args, cwd=str(ROOT), capture_output=True, text=True)
+    res = subprocess.run(
+        ["git"] + args,
+        cwd=str(ROOT),
+        capture_output=True,
+        text=True,
+        encoding="utf-8",
+        errors="replace",
+    )
     return res.returncode, res.stdout, res.stderr
 
 def get_base_commit() -> str | None: