Rename FABRIC series: FABRIC.md->0, FABRIC-2.md->1, FABRIC-3.md->2, FABRIC-4.md unchanged

FABRIC.md -> FABRIC-0.md
FABRIC-2.md -> FABRIC-1.md
FABRIC-3.md -> FABRIC-2.md (the current/living document)
FABRIC-4.md unchanged (new #3 to follow separately)

Every cross-reference repo-wide updated to match, including doc-comment
citations inside kernel source (.c/.h) files -- done via an ordered
placeholder substitution (FABRIC-3.md->placeholder2, FABRIC-2.md->
placeholder1, FABRIC.md->placeholder0, then placeholders resolved to
final names) in a single pass per file to avoid double-shifting
already-renamed references.

One line in capsules/font.4th grew past the 64-char block-format limit
as a side effect of the longer filename; shortened it and reverified
with mkcapsule --lint (34/34 pass) before rebuilding.

Verified 3-arch boot to ok> (amd64/aarch64/riscv64, each in the
foreground) after the fix; logs and DoE CSVs from this session's
verification runs included per this repo's own audit-artifact
convention.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019YcT3H2PQeyujrzjqS3Var

src/starkernel/usb/blkio_usb.c

@@ -92,7 +92,7 @@ static int usb_blk_info(blkio_dev_t *dev, blkio_info_t *out) {
     out->phys_sector_size = s->scsi_block_size;
     out->phys_size_bytes  = (uint64_t)s->total_forth_blocks * BLKIO_FORTH_BLOCK_SIZE;
     out->read_only        = 0; /* WRITE(10) verified live end-to-end on amd64,
-                                 * 2026-08-28 (FABRIC-3.md §F.1): BLK-CONFIRM-FORMAT's
+                                 * 2026-08-28 (FABRIC-2.md §F.1): BLK-CONFIRM-FORMAT's
                                  * BAM/reloc writes and an explicit content write both
                                  * survived a cold reboot and read back correctly. */
     return BLKIO_OK;