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>

src/helpers/ui/DisplayDriver.h

@@ -33,8 +33,8 @@ public:
   virtual uint16_t getTextWidth(const char* str) = 0;
   virtual int getCharWidth() const { return 6; }   // typical character advance width (px)
   virtual int getLineHeight() const { return 8; }  // pixel rows per text line
-  virtual void setLemonFont(bool) { }              // no-op; overridden by displays that support Lemon
-  virtual bool isLemonFont() const { return false; }
+  virtual void setSingleFont(bool) { }              // no-op; both concrete drivers are permanently pinned to their one font
+  virtual bool isSingleFont() const { return false; }
   // Layout helpers — derived from font metrics and screen size.
   // Use these instead of hardcoded pixel values so layouts adapt to any display.
   int lineStep()             const { return getLineHeight() + 2; }         // row pitch: text + gap