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

include/starkernel/plic.h

@@ -7,7 +7,7 @@
 /**
  * plic.h - Platform-Level Interrupt Controller interface (riscv64 only)
  *
- * Item 4.3.5a (FABRIC.md §27.5): Phase 0 (0.2/0.3) only ever enabled the
+ * Item 4.3.5a (FABRIC-0.md §27.5): Phase 0 (0.2/0.3) only ever enabled the
  * S-mode *timer* interrupt (sie.STIE). External interrupts (sie.SEIE) were
  * never touched, and the PLIC -- the only external-interrupt path on
  * RISC-V, there is no legacy PIC or I/O APIC equivalent -- had no driver