Add Chinese text rendering support

Extend the bitmap font pipeline with the Chinese Joker glyph subset and encode supported UTF-8 text for Tonc TTE. Move the affine map clear of the expanded font, add a compile-time VRAM overlap guard, and cover every custom glyph with host tests.

include/chinese_text.h

@@ -0,0 +1,21 @@
+/**
+ * @file chinese_text.h
+ * @brief UTF-8 conversion helpers for the extended TTE font.
+ */
+#ifndef CHINESE_TEXT_H
+#define CHINESE_TEXT_H
+
+#include <stddef.h>
+
+/**
+ * @brief Map supported UTF-8 Chinese text to valid UTF-8 sequences for custom TTE glyphs.
+ *
+ * ASCII bytes, including TTE formatting tags, are copied unchanged. Unsupported Unicode
+ * characters are replaced with '?'. Custom glyph IDs are emitted as UTF-8 because Tonc TTE
+ * decodes every byte above 0x7F as part of a UTF-8 sequence.
+ *
+ * @return Number of encoded bytes, excluding the null terminator.
+ */
+size_t chinese_text_encode(const char* utf8, char* output, size_t output_size);
+
+#endif // CHINESE_TEXT_H