Promote Xevious (U) and Zanac (U) from _wip/ to NROM/

- Xevious (U): Promoted from _wip/NROM/Xevious (U)/ to NROM/Xevious (U)/
  - Pass 3 complete: 34.5% code coverage, 143 semantic entry points,
    4 named data tables, ~20 semantic ZP aliases
  - NROM mapper 0, 32 KB PRG, 8 KB CHR, horizontal mirroring

- Zanac (U): Promoted from _wip/UNROM/Zanac (U)/ to NROM/Zanac (U)/
  - Pass 3 complete: 34.5% code coverage (bank 7 only), 133 semantic
    entry points, 26 named data tables, 14 semantic ZP aliases
  - UNROM mapper 2, 128 KB PRG (8 banks), no CHR
  - Bank 7 fixed at CPU -; banks 0-6 switchable at 000-
  - Bank 7 assembled separately as prg.07.s with .org

Both projects build byte-identical. Updated root README.md inventory,
per-project details, and WIP.md accordingly.

Move Zanac (U) to UNROM/ mapper directory

Zanac (U) is a UNROM (mapper 2) game, not NROM (mapper 0). Move it to
the correct mapper directory and update README.md and WIP.md references
accordingly. Update project counts in WIP.md (857->856 total, UNROM
98->97 projects).

Promote Mermaids of Atlantis (U) from _wip/ to MAPPER8/

Additional cleanup of Mermaids of Atlantis

UNROM/Zanac (U)/Makefile

@@ -0,0 +1,25 @@
+CA65 ?= ca65
+LD65 ?= ld65
+
+all: reconstructed.nes verify
+
+header.o: header.s header.bin
+	$(CA65) -g -o $@ $<
+
+prg0.o: prg.s symbols.inc locals.inc
+	$(CA65) -g -o $@ $<
+
+prg07.o: prg.07.s symbols.inc locals.inc
+	$(CA65) -g -o $@ $<
+
+reconstructed.nes: header.o prg0.o prg07.o linker.cfg
+	$(LD65) -C linker.cfg -m reconstructed.map -Ln reconstructed.lbl -o $@ header.o prg0.o prg07.o
+
+verify: reconstructed.nes rom.nes
+	cmp reconstructed.nes rom.nes
+	@echo "Byte-identical ROM verified."
+
+clean:
+	rm -f *.o reconstructed.nes reconstructed_prg.bin reconstructed.map reconstructed.lbl prg.07.bin prg.07.cfg
+
+.PHONY: all verify clean