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

tools/mkcapsule.c

@@ -221,7 +221,7 @@ static void sign_capsule_bytes(const uint8_t *data, size_t len,
  * init.4th (bare) is Mama's canonical init — gets FLAG_MAMA_INIT only.
  * Anything under capsules/contrib/ (name starts with "contrib:") gets
  * FLAG_CONTRIB in addition to the usual PRODUCTION|EXPERIMENT pair
- * (FABRIC-3.md §I.5, 2026-09-04) — path-match, mirrors FLAG_MAMA_INIT's
+ * (FABRIC-2.md §I.5, 2026-09-04) — path-match, mirrors FLAG_MAMA_INIT's
  * own exact-match pattern one line up, just prefix instead of exact.
  * All other capsules carry both FLAG_PRODUCTION and FLAG_EXPERIMENT so
  * that birth eligibility is not gated on mode type (D2).
@@ -242,7 +242,7 @@ static uint32_t flags_from_name(const char *name) {
 }
 
 /*
- * Magic-number content-type detection (FABRIC-3.md §I.4, FABRIC-2.md
+ * Magic-number content-type detection (FABRIC-2.md §I.4, FABRIC-1.md
  * Section U item 14). mkcapsule's own header comment has long said "the
  * file extension is preserved verbatim and is meaningful only at load
  * time" -- nothing has ever checked that a file's actual bytes match
@@ -513,7 +513,7 @@ static int process_file(const char *fpath, const struct stat *sb,
         }
     }
 
-    /* Magic-number content-type cross-check (FABRIC-3.md §I.4) --
+    /* Magic-number content-type cross-check (FABRIC-2.md §I.4) --
      * WARN-only, never refuses; UNKNOWN on either side means "no
      * expectation," not a mismatch. */
     {