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/capsule_birth.h

@@ -127,7 +127,7 @@ CapsuleRunResult capsule_birth_mama(
  * @param descs         Capsule descriptor array
  * @param names         Capsule name entry array (parallel to descs)
  * @param arena         Capsule payload arena
- * @param parent        Who is birthing this VM (FABRIC-3.md §H.12 step 7) --
+ * @param parent        Who is birthing this VM (FABRIC-2.md §H.12 step 7) --
  *                       the caller's own VMUuid (e.g. vm->stadium_vm_id for
  *                       a FORTH word handler), recorded on the new VM's
  *                       Session.parent. Every current call site has one in
@@ -138,7 +138,7 @@ CapsuleRunResult capsule_birth_mama(
  * @param skip_pki_sig  0 for every build-time capsule (the normal case --
  *                       checked against the compile-time-baked signature
  *                       array via capsule_get_signatures()). Non-zero only
- *                       for RUNCAP (FABRIC-3.md §F.6/F.18): a heap-built,
+ *                       for RUNCAP (FABRIC-2.md §F.6/F.18): a heap-built,
  *                       single-entry directory sourced from a user's own
  *                       thumbdrive has no entry in that array at all --
  *                       index 0 would silently compare against whatever
@@ -254,7 +254,7 @@ uint32_t capsule_vm_registry_count(void);
  * capsule_vm_registry_get_by_index - Get registry entry by list position
  * (birth order, stable within a boot session -- the registry is
  * append-only). For enumeration (e.g. the idle-loop messaging pump,
- * FABRIC-3.md Phase C, 2026-08-28), where no vm_id is known up front.
+ * FABRIC-2.md Phase C, 2026-08-28), where no vm_id is known up front.
  * Index range is [0, capsule_vm_registry_count()).
  *
  * @param index  Zero-based position in birth order