term: 40-column text terminal on the CGB LCD (4x8 dynamic tiles)

Add a background-tile text terminal that packs TWO 4px-wide characters
into each 8x8 tile, giving a 40x18 grid instead of the 20x18 you'd get
from an 8x8 font. The tilemap is static (one dedicated VRAM tile per
screen position); we rebuild a tile's 16 bytes from two glyphs whenever
a character changes. 360 tiles exceed the 256 a single tilemap can
address, so positions 256-359 live in VRAM bank 1 via the CGB tilemap
attribute bank-bit -- hence CGB-only.

- Switch the ROM to CGB (rgbfix -C). Safe for the FS: every process has
  PROC_WRAMB=1, so SVBK stays on bank 1 and the WRAMX FS caches don't move.
- CGB BG palette 0 = white bg / black text via BCPS/BCPD.
- src/term.asm: term_init (palette + static tilemap + clear buffer),
  build_tile (combine two 4px glyphs -> one 8x8 tile, correct VRAM bank),
  term_redraw (rebuild all tiles), term_puts, term_show, term_test.
- src/font.asm: 96-glyph 3x5-in-4x8 font, generated by tools/genfont.py.
- 40x18 text buffer at $D600 (WRAMX, above the FS caches).
- tools/ppmview.py: render a --shot PPM as ASCII so the LCD is inspectable
  from the shell during development.

Verified via emulator screenshot: "GBOS TERMINAL", the alphabet, and a
bank-1 row all render legibly at 40 columns. Serial shell + filesystem
still work unchanged.

Note: a full term_redraw builds 360 tiles and takes ~8 frames; fine for
incremental single-char updates, but scrolling needs a smarter path
(next milestone). Input (no keyboard) is also still TODO.

1 files changed, 1 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 58a6bd1..b7fe95d 100644
--- a/Makefile
+++ b/Makefile
@@ -8,7 +8,7 @@ OBJS     := $(patsubst src/%.asm,$(BUILD)/%.o,$(SRCS))
 
 ASFLAGS  := -I include -Wall
 # MBC5 + RAM + battery; -r 3 = 32 KiB cart RAM (bump for more task banks)
-FIXFLAGS := -v -m MBC5+RAM+BATTERY -r 4 -p 0xFF -t GBOS
+FIXFLAGS := -v -C -m MBC5+RAM+BATTERY -r 4 -p 0xFF -t GBOS
 
 .PHONY: all clean run