refactor: group scripts into walker/ wikigen/ bundle/

Organize the 16 loose scripts by concern:
  walker/  -- .wbt save tooling (sand, build_wbt, walker_hashes,
              harvest_hashes, recover_key)
  wikigen/ -- MediaWiki page generators (make_*_wiki, render_wiki)
  bundle/  -- Unity/Odin asset extraction (unitybundle, odin_read,
              extract_*, loot_probe, dump_loot_bytes)

The only cross-script imports (build_wbt->walker_hashes,
extract_loot->odin_read) live within the same folder, so each
script's dir on sys.path[0] keeps them resolving with no code
changes. All data paths are absolute, so the moves don't affect
I/O. Named the code dir wikigen/ to avoid colliding with the
generated wiki/ output dir; ignore the regenerable wiki_site/ render.

.gitignore

@@ -9,6 +9,9 @@ snapshots/
 # Huge IL2CPP / GameAssembly dumps (regenerable, ~460MB)
 /il2cpp/
 
+# Local HTML render of the wiki (regenerable via wikigen/render_wiki.py)
+/wiki_site/
+
 # Python
 __pycache__/
 *.py[cod]