fix(skills): preserve non-ASCII characters in skill frontmatter (#2917)

* fix(skills): preserve non-ASCII chars in skill frontmatter

Skill SKILL.md frontmatter descriptions containing non-ASCII
characters were escaped to \uXXXX / \xXX sequences because
yaml.safe_dump() was called without allow_unicode=True.

- Add allow_unicode=True to the 7 skill/command frontmatter
  safe_dump sites (extensions, presets, claude integration)
- Add regression tests for the render and extension-install paths

Follows the approach of #1936; encoding="utf-8" is already set on
the affected write paths, so no encoding change is needed here.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* refactor(_utils): add dump_frontmatter helper

Centralize skill/command frontmatter YAML serialization into a single
_utils.dump_frontmatter helper so no call site can drop allow_unicode or
diverge on formatting. Route the 7 existing sites through it and drop a
now-unused local yaml import.

Switch the extension test fixtures to yaml.safe_dump for parity with the
production safe-dump/safe-load codepaths.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/specify_cli/_utils.py

@@ -8,6 +8,7 @@ import shutil
 import stat
 import subprocess
 import tempfile
+import yaml
 from pathlib import Path
 from typing import Any
 from ._console import console
@@ -16,6 +17,16 @@ CLAUDE_LOCAL_PATH = Path.home() / ".claude" / "local" / "claude"
 CLAUDE_NPM_LOCAL_PATH = Path.home() / ".claude" / "local" / "node_modules" / ".bin" / "claude"
 
 
+def dump_frontmatter(data: dict[str, Any]) -> str:
+    """Serialize skill/command frontmatter to a YAML string.
+
+    Centralizes the dump options used for SKILL.md frontmatter: ``allow_unicode``
+    preserves Unicode descriptions and ``sort_keys=False`` keeps key order, so no
+    call site can silently drop either.
+    """
+    return yaml.safe_dump(data, sort_keys=False, allow_unicode=True).strip()
+
+
 def run_command(cmd: list[str], check_return: bool = True, capture: bool = False, shell: bool = False) -> str | None:
     """Run a shell command and optionally capture output."""
     try: