Phase 5 corrections: sharpen 5.1's boundary claim, fix hosted Makefile's own stale VERSION

Advisor review of the Phase 5 close-out commit caught two real issues:

- Task 5.1's write-up claimed the Isabelle pass "confirms no regression" --
  overstated. Nothing in proof/'s scope changed, so the pass isn't
  regression evidence, it's a build-completeness formality; the boundary
  argument alone already supports the real conclusion. Sharpened.

- sbom.spdx was regenerated before the 5.4 version bump, so it briefly
  understated the engine version. Root cause: the hosted Makefile carries
  its own separate hardcoded VERSION (Makefile:17, still 3.1.0), distinct
  from Makefile.starkernel's copy that 5.4 bumped -- duplication CLAUDE.md's
  own "two independently tracked version strings" note doesn't document.
  Bumped to 3.2.0 to match, regenerated (PackageVersion now correct), and
  rebuilt the hosted starforth binary so lfs/amd64/starforth reflects it.

Also recorded why 5.1-5.4 landed as one commit (deviation from this
document's per-task-commit discipline) and sharpened the riscv64 log
entry so the FAILED run and the accepted retry aren't ambiguous to a
future reader grepping logs/.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

sbom.spdx

@@ -2,11 +2,11 @@ SPDXVersion: SPDX-2.3
 DataLicense: CC0-1.0
 SPDXID: SPDXRef-DOCUMENT
 DocumentName: LithosAnanke
-DocumentNamespace: https://anchore.com/syft/dir/LithosAnanke-2eaf09a2-c24c-435e-b628-e0dc58035114
+DocumentNamespace: https://anchore.com/syft/dir/LithosAnanke-d51dd61a-7347-4290-89f9-8896251d48fc
 LicenseListVersion: 3.28
 Creator: Organization: Anchore, Inc
 Creator: Tool: syft-1.52.0
-Created: 2026-09-22T23:21:56Z
+Created: 2026-09-22T23:48:18Z
 
 ##### Unpackaged files
 
@@ -42,7 +42,7 @@ FileCopyrightText: NOASSERTION
 
 PackageName: LithosAnanke
 SPDXID: SPDXRef-DocumentRoot-Directory-LithosAnanke
-PackageVersion: 3.1.0
+PackageVersion: 3.2.0
 PackageSupplier: NOASSERTION
 PackageDownloadLocation: NOASSERTION
 PrimaryPackagePurpose: FILE