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/arch/aarch64/apic.c

@@ -16,7 +16,7 @@
  *
  * Base addresses and the PPI INTID are QEMU-virt-machine constants, not
  * device-tree-discovered, and that is a deliberate, recorded exception
- * rather than an oversight (FABRIC.md item 0.6, GAP-B1 follow-up):
+ * rather than an oversight (FABRIC-0.md item 0.6, GAP-B1 follow-up):
  * `fdt_valid(boot_info->dtb)` fails on this system's aarch64 firmware
  * (qemu-efi-aarch64 2025.11-3ubuntu7 does not forward a devicetree to the
  * guest), confirmed live rather than assumed. The values below were not
@@ -168,7 +168,7 @@ int apic_init(BootInfo *boot_info)
  * 3. @c GICD_ITARGETSR (byte-indexed like IPRIORITYR) -- routes to CPU 0
  *    only; this target has no @c -smp, so no other bit is ever valid.
  * 4. @c GICD_ICFGR is read back, not written, unless the readback disagrees
- *    with the expected level-triggered configuration -- FABRIC.md §27.5.1's
+ *    with the expected level-triggered configuration -- FABRIC-0.md §27.5.1's
  *    decoded QEMU `interrupt-map` says PCI legacy INTx on this board already
  *    is level-triggered by default, so this keeps item 0.6's "don't touch
  *    ICFGR unless forced to" posture rather than writing it unconditionally.