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/alembic/versions/0106_api_tokens.py

@@ -89,7 +89,22 @@ def downgrade() -> None:
     op.drop_table("api_token_grants")
     op.drop_table("api_tokens")
     op.drop_index("uq_file_folder_hub", table_name="file_folders")
-    # A Hub folder may hold files (their foreign key RESTRICTs a delete): it becomes an own folder.
-    op.execute("UPDATE file_folders SET kind = 'own', name = 'Hub ' || id WHERE kind = 'hub'")
+    # A Hub folder may hold files (their foreign key RESTRICTs a delete): it becomes an own folder,
+    # named "Hub <id>" — or "Hub <id> (2)", … when its user already has a folder of that name,
+    # which `uq_file_folder_own_name` (per user, case-blind) would refuse.
+    conn = op.get_bind()
+    hubs = conn.execute(sa.text("SELECT id, user_id FROM file_folders WHERE kind = 'hub'")).all()
+    for folder_id, user_id in hubs:
+        name, n = f"Hub {folder_id}", 1
+        while conn.execute(
+            sa.text("SELECT 1 FROM file_folders WHERE user_id = :u AND lower(name) = lower(:n)"),
+            {"u": user_id, "n": name},
+        ).first():
+            n += 1
+            name = f"Hub {folder_id} ({n})"
+        conn.execute(
+            sa.text("UPDATE file_folders SET kind = 'own', name = :n WHERE id = :i"),
+            {"n": name, "i": folder_id},
+        )
     op.drop_constraint("ck_file_folder_kind", "file_folders", type_="check")
     op.create_check_constraint("ck_file_folder_kind", "file_folders", _KIND_OLD)