Move web UI from /ui/ to /web/ path prefix

The web UI is now mounted at /web/ (previously /ui/) — cmd/server/main.go
wraps web.Server.Handler with http.StripPrefix("/web", ...), so
internal/web's own routes stay unprefixed (/, /login, /logout,
/shares/..., /static/...) and only the outer mux adds the prefix. All
templates, redirects, and cookie paths updated accordingly. The root '/'
route reverts to the original unauthenticated welcome page (linking to
/web/), and /cal/, /card/, /files/ are unaffected.

Also gitignore the bin/ build output directory.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

internal/web/shares.go

@@ -10,7 +10,7 @@ import (
 
 // handleCalendarShare handles POST (create/update share) and DELETE
 // (revoke share) for the current user's calendars, mounted at
-// /ui/shares/calendar. htmx sends the resource + shared_with (+ permission
+// /shares/calendar. htmx sends the resource + shared_with (+ permission
 // for POST) as form values and expects the updated resource card HTML
 // back for an out-of-band swap.
 func (s *Server) handleCalendarShare(w http.ResponseWriter, r *http.Request) {