docs: v0.112.0 CHANGELOG + README (registry access modes) + REUSE (runner vars seam, WWW-Authenticate parser)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PSK5g6qYLknKj8u3QAFEr6

REUSE.md

@@ -26,7 +26,8 @@
 | `rsyncCopy` | controller/internal/stacks/migrate.go | `(ctx, src, dst, onBytes)` | Additive copy (migration/moves) | `-a --checksum`, NEVER `--delete`; progress2 byte callback; ctx timeout |
 | `rsyncVerify` | controller/internal/stacks/migrate.go | `(ctx, src, dst) error` | Post-copy verification | Dry-run `-ani`; fails on any pending content transfer; attr-only lines ignored |
 | `walkMerge` | controller/internal/stacks/migrate.go | `(lg, srcNS, dstNS, skip, assertOnly, onBytes)` | Collision-safe userdata merge | Renames to lowest-free sibling on content mismatch; additive |
-| `runCommand` / `runCommandStdin` | controller/internal/selfupdate/updater.go | `(name, args...) (string, error)` | docker CLI in updater | stdin variant for `docker login --password-stdin` (no secret in argv) |
+| `runCommand` / `runCommandStdin` | controller/internal/selfupdate/updater.go | `(name, args...) (string, error)` | docker CLI in updater | stdin variant for `docker login --password-stdin` (no secret in argv); package VARS since v0.112.0 — override in tests (fakeRunner in registry_anon_test.go) |
+| `parseWWWAuthenticate` + `fetchAnonymousToken` | controller/internal/selfupdate/updater.go | Bearer-challenge parse + anonymous Docker v2 token | Any credential-free registry API access | realm comes FROM THE HEADER (never hardcode a token URL); denial = errAnonymousDenied, never "credentials missing" |
 | `Syncer.runGit` / `runGitInDir` | controller/internal/sync/sync.go | `(args...) error` | git CLI ops | Credentials masked in logs via `maskRepoURL` |
 
 ### HTTP/JSON envelopes + flash messages