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/presets/__init__.py

@@ -30,6 +30,7 @@ from packaging.specifiers import SpecifierSet, InvalidSpecifier
 from ..extensions import REINSTALL_COMMAND, ExtensionRegistry, normalize_priority
 from .._init_options import is_ai_skills_enabled
 from ..integrations.base import IntegrationBase
+from .._utils import dump_frontmatter
 
 
 def _substitute_core_template(
@@ -1068,7 +1069,7 @@ class PresetManager:
                         skill_name, desc,
                         f"override:{cmd_name}",
                     )
-                    fm_text = yaml.safe_dump(fm_data, sort_keys=False).strip()
+                    fm_text = dump_frontmatter(fm_data)
                     skill_title = self._skill_title_from_command(cmd_name)
                     skill_content = (
                         f"---\n{fm_text}\n---\n\n"
@@ -1345,7 +1346,7 @@ class PresetManager:
                     enhanced_desc,
                     f"preset:{manifest.id}",
                 )
-                frontmatter_text = yaml.safe_dump(frontmatter_data, sort_keys=False).strip()
+                frontmatter_text = dump_frontmatter(frontmatter_data)
                 skill_content = (
                     f"---\n"
                     f"{frontmatter_text}\n"
@@ -1441,7 +1442,7 @@ class PresetManager:
                     enhanced_desc,
                     f"templates/commands/{short_name}.md",
                 )
-                frontmatter_text = yaml.safe_dump(frontmatter_data, sort_keys=False).strip()
+                frontmatter_text = dump_frontmatter(frontmatter_data)
                 skill_title = self._skill_title_from_command(short_name)
                 skill_content = (
                     f"---\n"
@@ -1478,7 +1479,7 @@ class PresetManager:
                     frontmatter.get("description", f"Extension command: {command_name}"),
                     extension_restore["source"],
                 )
-                frontmatter_text = yaml.safe_dump(frontmatter_data, sort_keys=False).strip()
+                frontmatter_text = dump_frontmatter(frontmatter_data)
                 skill_content = (
                     f"---\n"
                     f"{frontmatter_text}\n"
@@ -3276,7 +3277,7 @@ class PresetResolver:
             if top_fm:
                 top_frontmatter_text = (
                     "---\n"
-                    + yaml.safe_dump(top_fm, sort_keys=False).strip()
+                    + dump_frontmatter(top_fm)
                     + "\n---"
                 )
             else: