fix(config): write config.yaml as UTF-8 to stop emoji/personality corruption (#51676)

atomic_yaml_write (and two sibling config writers) called yaml.dump
without allow_unicode=True. The default personalities shipped in cli.py
contain emoji/kaomoji, so PyYAML escaped astral-plane chars as 8-digit
\\UXXXXXXXX sequences inside multi-line double-quoted strings wrapped
with \\ line-continuations. Stricter/non-PyYAML parsers, editors, and
hand-edits break that structure into unclosed quotes, failing the whole
config parse -> silent fallback to defaults -> custom_providers lost.

Add allow_unicode=True to the canonical writer plus tui_gateway/server.py
and the telegram adapter's atomic config write so config is written as
readable UTF-8 with no escape/fold artifacts.

Fixes #51356

utils.py

@@ -211,7 +211,20 @@ def atomic_yaml_write(
     )
     try:
         with os.fdopen(fd, "w", encoding="utf-8") as f:
-            yaml.dump(data, f, default_flow_style=default_flow_style, sort_keys=sort_keys)
+            # allow_unicode=True writes emoji/kaomoji (e.g. personalities, skin
+            # cursors) as real UTF-8 instead of fragile escape sequences. Without
+            # it, PyYAML emits astral-plane chars as `\UXXXXXXXX` (8-digit) escapes
+            # inside multi-line double-quoted strings wrapped with `\`
+            # continuations — a structure that stricter/non-PyYAML parsers and
+            # hand-edits routinely break into unclosed quotes, corrupting the whole
+            # config (GitHub #51356).
+            yaml.dump(
+                data,
+                f,
+                default_flow_style=default_flow_style,
+                sort_keys=sort_keys,
+                allow_unicode=True,
+            )
             if extra_content:
                 f.write(extra_content)
             f.flush()