docs(status): correct stale subsystem states against the source

STATUS.md/TASKBOARD.md under-reported several subsystems that are in fact
implemented. Corrected against the code and against a clean QEMU boot log
(.build_tmp/qemu_final.log, this branch).

- 页表映射接口 was ⬜ "mmio 通用映射待做". It exists and is in use:
  kernel_api.mm_map_mmio / mm_unmap_mmio (PCD|PWT independent window), called
  by apic, ehci, xhci and nvme, including BARs above 4G. -> ✅

- NVMe was 🔶 "PCI discovery only, BAR0>4G 待映射". CODE/DKM/nvme/nvme.c is
  1641 lines: admin SQ/CQ with phase bit, IDENTIFY, IO queue (qid=1), read/
  write/flush, cross-page PRP lists, MSI and MSI-X (vector allocator, IDT pool
  0x40-0xDF), block provider registration, NVME-E01..E03 zero-fallback
  instrumentation. -> ✅

- virtio_net was 🔶 "PCI/capability 枚举, 无 virtqueue". It has a legacy
  split-ring virtqueue (desc/avail/used), vq_setup, 32x2048B RX buffers, TX/RX
  rings and a DHCP DISCOVER->OFFER selftest. -> ✅

- ELF64 .drv loading said 14/14. build.ps1 now compiles all 17 drivers listed
  in manifest.json (fixed on this branch; nine were never built since 055c521
  untracked the .drv binaries). -> 17/17

- FAT32 (DKM side) stays 🔶 but the boundary was wrong. It is read-only
  BPB/FAT/dirent parsing plus a root-directory walk, with no filesystem API
  layer (no open/read/stat) - not "子目录路径待完善". The large-disk read/write
  path lives in the DSK-side FAT32 implementation.

- TASKBOARD 遗留工程债: vector allocator/MSI-X, NVMe high BAR MMIO and
  virtio-net virtqueue RX/TX are done. The remaining FAT32 item is reworded to
  what is actually missing (the FS API layer).

Evidence for the driver/NVMe/virtio rows is the boot log on this branch:
14x "[<drv>] driver ready", and with no NVMe controller / virtio-net device
attached the drivers correctly log a warning and still reach "driver ready"
(designed fallback, both listed in the CLAUDE.md whitelist).

docs/TASKBOARD.md

@@ -48,8 +48,8 @@
 
 ## 遗留工程债（Phase 存档，非五期编号）
 
-- [ ] Vector allocator / MSI-X
-- [ ] NVMe 高位 BAR MMIO（BAR0>4G）
-- [ ] virtio-net virtqueue RX/TX
-- [ ] FAT32 完整子目录路径解析（DKM 侧）
+- [x] Vector allocator / MSI-X（NVMe 使用 IDT 向量池 0x40–0xDF + MSI-X 表项编程）
+- [x] NVMe 高位 BAR MMIO（BAR0>4G，`mm_map_mmio` 独立窗口映射）
+- [x] virtio-net virtqueue RX/TX（legacy split-ring + DHCP selftest）
+- [ ] FAT32 文件系统 API 层（DKM 侧当前只有 BPB/目录 demo，无 open/read/stat）
 - [ ] DKM 零 warning + 统一 ABI 头