fix: consolidate kconsole banner + safe disk FS probe order

fix: consolidate kconsole banner + safe disk FS probe order

1. Consolidate redundant PANIC + kconsole banners into a single
   message shown by kconsole_enter(). Previously both main.c and
   kconsole.c printed separate banners.

2. Fix critical VFS mount ordering bug: diskfs, FAT, and ext2 all
   share the same ATA primary master disk at LBA 0. Previously
   diskfs_create_root() was called first, and its auto-format
   (diskfs_super_load) would overwrite LBA 2-3 if DISKFS_MAGIC
   was not found -- destroying any ext2 superblock at the same
   location. Now the probe order is:
     a) ext2 (checks magic 0xEF53 at byte 1080)
     b) FAT (validates BPB fields at LBA 0)
     c) diskfs (fallback, may auto-format blank disks)
   Only one FS is mounted per device -- they are mutually exclusive.

3. Make ata_pio_init_primary_master() idempotent with a static
   guard flag so it can be called from both init.c and
   diskfs_create_root() without double-initializing.

4. Increase VFS mount table from 8 to 16 slots to prevent
   -ENOSPC when adding future mount points.

Build: clean, cppcheck: clean, smoke: 19/19 pass