fix(files): ending every session ends every API token, and the share links hold their folder

- A password reset or change, "log out everywhere" and a revoked untrusted password revoke all of the
  account's API tokens too (audited): one minted from a stolen session no longer outlives the answer.
- A bearer token or link grant with a non-ASCII character is refused (401/403), not a 500.
- Making a token's grants or a folder link holds the folder, so a racing delete cannot fail the
  foreign key; a link's view count is one atomic UPDATE.
- A folder link's card counts exactly the files its page lists (one `links.folder_files`).
- A file with no extension is served without a trailing dot.
- 0106's downgrade names a Hub folder so it never collides with one of the user's folders.
- The speed baseline reads share tokens through the app (the database keeps them hashed/encrypted).
- Tests: the token scope on the real session stack, the folder poster, the Hub refused for a link,
  0106's downgrade data step, 0107 without a key; docs/comments follow (three folder kinds, folder
  links, key change, the cleanup job's token warnings).

backend/app/audit.py

@@ -73,7 +73,8 @@ class AuditAction:
     # What a token then did is the file rows above, their summary naming it.
     API_TOKEN_CREATE = "api_token_create"
     API_TOKEN_REVOKE = "api_token_revoke"
-    # A public `/watch` link to a file (`routes.downloads`): made, its settings changed, revoked.
+    # A public `/watch` link to a file or a folder (`routes.downloads`): made, its settings changed,
+    # revoked.
     # Never its token or password — only whether it has one.
     DOWNLOAD_LINK_CREATE = "download_link_create"
     DOWNLOAD_LINK_UPDATE = "download_link_update"