Fix regular expression: Repository name can not start with .-_
Aligning the naming constraints with git.sr.ht:
- repository name must be at least one character, not two;
- fist character can be uppercase (but not a numeric);
- in general accepts only alphanumeric characters or ._-

Fix editing of labels with / in the name
Implement editing labels

as requested in https://todo.sr.ht/~sircmpwn/todo.sr.ht/159
Fix recent users function

A bug was introduced when modifying the functions to work with
participants in b4c92a39. A new field was added to the query, but the
offset was not modified when reading the username.
Set ticket title and description with URL params

Setting ?title=foo&description=bar to the tracker page will
automatically populate the title and description inputs. This can be
useful for crafting error-reporting links.
Make ticket timestamp a permalink
Add a build manifest for Debian packaging
Add In-Reply-To header to notification emails

We add a Message-ID header to the notification email about new ticket,
the value of ticket's mailing list is used. For other notifications, we
insert an In-Reply-To header with the same value. This implements "flat
replies" as described in https://todo.sr.ht/~sircmpwn/todo.sr.ht/97.

Closes https://todo.sr.ht/~sircmpwn/todo.sr.ht/97
Fix straggling by_user reference in events.html
Fix oversized images in event lists
Narrow the comments area
Use participant_url for rendering mentions
Use flexbox for wrapping ticket titles
Rearrange ticket detail pages
Correct "get_participant_by_user" -> "for_user"
Updates per core.sr.ht centered redesign
Fix enable/disable notifications
Allow owners to import comments from external host
Allow admins to create tickets at specific times