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.

.gitignore

@@ -6,5 +6,4 @@ immersive_paintings_cache/
 
 # Large or regenerable local artifacts
 *.tar.gz
-analysis/raw/
 analysis/client-perf/proposed-configs/out/