fix(cli): add allow_unicode=True and encoding="utf-8" to YAML I/O (#1936)

None of the yaml.dump() calls specify allow_unicode=True, causing
non-ASCII characters in extension descriptions to be escaped to
\uXXXX sequences in generated .agent.md frontmatter and config files.

Add allow_unicode=True to all 6 yaml.dump() call sites, and
encoding="utf-8" to all corresponding write_text() and read_text()
calls to ensure consistent UTF-8 handling across platforms.

src/specify_cli/presets.py

@@ -1062,8 +1062,8 @@ class PresetCatalog:
         if not config_path.exists():
             return None
         try:
-            data = yaml.safe_load(config_path.read_text()) or {}
-        except (yaml.YAMLError, OSError) as e:
+            data = yaml.safe_load(config_path.read_text(encoding="utf-8")) or {}
+        except (yaml.YAMLError, OSError, UnicodeError) as e:
             raise PresetValidationError(
                 f"Failed to read catalog config {config_path}: {e}"
             )