chore(analysis): archive finished reviews, drop stale duplicates

Move the completed 2026-09 candidate review (MODLIST-REVIEW/-GROUPS,
CANDIDATE-APPENDIX, PACK-CONTEXT), FINDINGS.md and the shipped FTB Chunks swap
write-up into analysis/archive/, with a README mapping their old paths. The
review's build pieces, subagent intermediates and Modrinth API dumps are
deleted: the assembled reports carry their content. MODLIST-GROUPS.md was a
byte-for-byte duplicate of analysis/groups-table.md.

Also: drop the now-pointless FINDINGS/MODLIST packwizignore lines (analysis/
covers the archive), and gitignore *.tar.gz so the 650 MB map-migration world
tarball can't be committed by accident.

.packwizignore

@@ -21,8 +21,6 @@ kubejs/
 local/
 
 # Authoring/review material - belongs in the repo, never in the pack
-FINDINGS.md
-MODLIST-*.md
 analysis/
 phase0/
 ftbbackups3/