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/timer.h

@@ -93,7 +93,7 @@ typedef struct time_trust_state {
                                      * read directly by mainline
                                      * (heartbeat_ticks()); genuinely
                                      * concurrent, unlike every other field in
-                                     * this struct (FABRIC.md item 4.5a/4.5b,
+                                     * this struct (FABRIC-0.md item 4.5a/4.5b,
                                      * 2026-08-11). */
     uint64_t     last_tsc;         /* TSC at last heartbeat */
     uint64_t     expected_delta;   /* Expected TSC ticks per heartbeat */
@@ -209,7 +209,7 @@ const TimeTrustState *heartbeat_state(void);
 
 /**
  * Set the adaptive re-arm period, in nanoseconds (punch-list item 0.8,
- * FABRIC.md §26). Called from the mainline execution path only (Loop #7's
+ * FABRIC-0.md §26). Called from the mainline execution path only (Loop #7's
  * site in vm_runtime.c) -- never from interrupt context. Clamped to
  * [1/4x, 4x] of the kernel's base period internally; a caller need not
  * pre-clamp.