Implement BSAVE/BLOAD, TUI color, extended PEEK/POKE, update to v0.12.0

BSAVE/BLOAD: save and load virtual memory blocks with 0xFD-header
binary format, operating on the current DEF SEG segment.

TUI color: tui_refresh emits ANSI SGR codes from cell attributes;
COLOR statement sets tui.current_attr when TUI is active.

Extended PEEK/POKE: CGA graphics framebuffer (interlaced layout) via
gfx_cga_peek/poke routed through virmem when gfx_active(); BIOS
keyboard shift flags (offset 0x17 bit 7 = insert mode).

Add bibliography to language reference. 64 tests, all passing.

tests/programs/bsave_bload.bas

@@ -0,0 +1,18 @@
+10 REM Test BSAVE and BLOAD via virtual memory
+20 REM In piped mode, B800 text buffer is inactive so values are 0
+30 REM This test verifies the BSAVE/BLOAD flow and file format
+40 DEF SEG = &HB800
+50 REM BSAVE 4 bytes (will be zeros in piped mode)
+60 BSAVE "BSTEST.BIN", 0, 4
+70 PRINT "BSAVE OK"
+80 REM BLOAD back to same offset
+90 BLOAD "BSTEST.BIN"
+100 PRINT "BLOAD OK"
+110 REM BLOAD with explicit offset
+120 BLOAD "BSTEST.BIN", 100
+130 PRINT "BLOAD OFFSET OK"
+140 REM Verify file was created and can be re-read
+150 DEF SEG
+160 KILL "BSTEST.BIN"
+170 PRINT "KILL OK"
+180 PRINT "DONE"