Add the PicoCalc visual system:
- MESH_THEME_16: 16-slot palette with deliberate RGB values for truecolor=False
- make_console(): picks theme based on platform.truecolor
- glyph(): central emoji→single-BMP-char mapping for the 512-glyph font
- Type-based name_style() and register_node_type() for PicoCalc colour (key→type)
- Text folding: fold_text() with NFKD accent stripping and emoji→placeholder
- Platform-aware icon rendering in packet_viewer, dashboard_screen, courier_screen
- Reception layer registers node types for colour lookup
- Gallery tests check truecolor constraint on PICOCALC
All 1239 tests pass; 13 xfail (P6 width worklist).
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>