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

tests/hermes_cli/test_atomic_yaml_write.py

@@ -41,3 +41,36 @@ class TestAtomicYamlWrite:
         text = target.read_text(encoding="utf-8")
         assert "key: value" in text
         assert "# comment" in text
+
+    def test_writes_unicode_unescaped_and_round_trips(self, tmp_path):
+        """Emoji/kaomoji are written as real UTF-8, not fragile escape sequences.
+
+        Regression for GitHub #51356: without allow_unicode=True, PyYAML emitted
+        astral-plane chars (emoji) as 8-digit `\\UXXXXXXXX` escapes inside
+        multi-line double-quoted strings wrapped with `\\` continuations, which
+        stricter/non-PyYAML parsers and hand-edits broke into unclosed quotes,
+        corrupting the entire config.
+        """
+        target = tmp_path / "config.yaml"
+        # Mirrors the default personalities + skin cursor shipped in cli.py.
+        data = {
+            "personalities": {
+                "kawaii": "kawaii desu~! (◕‿◕) ★ ♪ ヽ(>∀<☆)ノ",
+                "catgirl": "nya~! (=^･ω･^=) ฅ^•ﻌ•^ฅ",
+                "surfer": "Cowabunga! 🤙 totally rad bro",
+                "hype": "LET'S GOOOO!!! 🔥 LEGENDARY!",
+            },
+            "display": {"cursor": " ▉"},
+        }
+
+        atomic_yaml_write(target, data)
+
+        text = target.read_text(encoding="utf-8")
+        # No escape artifacts of any kind — real characters on disk.
+        assert "\\U" not in text
+        assert "\\u" not in text
+        # Real glyphs are present verbatim.
+        assert "🔥" in text
+        assert "(=^･ω･^=)" in text
+        # And it reloads to exactly what was written.
+        assert yaml.safe_load(text) == data