chore: pre-release cleanup pass (Lemon-era naming, bot sender parsing dedup)

Renamed the vestigial Lemon/default font-switch naming (setLemonFont/
isLemonFont/drawLemonChar/lemonXAdvance/_use_lemon -> setSingleFont/
isSingleFont/drawGlyph/glyphXAdvance/_single_font) across DisplayDriver.h
and both concrete drivers -- both have been permanently single-font for
several commits, so the old names invited a future reader to think a
real switch still existed. Pure identifier rename, no logic changed.

Also extracted the byte-identical "SenderName: " prefix-splitting in
MyMeshBot.h's tryBotReplyChannel()/tryBotChannelCommand() into a shared
botChannelSenderSplit(), mirroring the existing botRoomSenderName().

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

examples/companion_radio/MyMesh.h

@@ -328,6 +328,11 @@ private:
   // Resolves a room post's signed author prefix to a display name for {name};
   // falls back to a generic label when the poster isn't a known contact.
   void botRoomSenderName(const uint8_t* sender_prefix, char* out, int out_len);
+  // Splits a channel message's leading "SenderName: " text convention off its
+  // body, for the {name} placeholder and to match triggers/commands against
+  // the body only. `*msg_out` points into `text` (no copy); `sender_name`
+  // defaults to "someone" if there's no ": " separator.
+  void botChannelSenderSplit(const char* text, char* sender_name, int sender_name_len, const char** msg_out);
 
   void writeOKFrame();
   void writeErrFrame(uint8_t err_code);