Fix various trivial problems (#32861)

1. add/improve comments to help future readers could understand the
problem more easily.
2. add an error log to LDAP with username fallback
3. use `or` instead of `Iif` for "repo/branch_dropdown" (`Iif` was a
mistake, but it doesn't really affect the UI)
4. add `tw-font-mono` style to container digest to match dockerhub
5. fix a bug in RepoBranchTagSelector: the form is not updated when
there is no click to an item

---------

Co-authored-by: delvh <dev.lh@web.de>

templates/user/auth/signin_inner.tmpl

@@ -48,6 +48,7 @@
 			</div>
 		</form>
 		{{end}}{{/*if .EnablePasswordSignInForm*/}}
+		{{/* "oauth_container" contains not only "oauth2" methods, but also "OIDC" and "SSPI" methods */}}
 		{{$showOAuth2Methods := or .OAuth2Providers .EnableOpenIDSignIn .EnableSSPI}}
 		{{if and $showOAuth2Methods .EnablePasswordSignInForm}}
 			<div class="divider divider-text">{{ctx.Locale.Tr "sign_in_or"}}</div>

templates/user/auth/signup_inner.tmpl

@@ -47,6 +47,8 @@
 					</button>
 				</div>
 			{{end}}
+			{{/* "oauth_container" contains not only "oauth2" methods, but also "OIDC" and "SSPI" methods */}}
+			{{/* TODO: it seems that "EnableSSPI" is only set in "sign-in" handlers, but it should use the same logic to control its display */}}
 			{{$showOAuth2Methods := or .OAuth2Providers .EnableOpenIDSignIn .EnableSSPI}}
 			{{if $showOAuth2Methods}}
 				<div class="divider divider-text">{{ctx.Locale.Tr "sign_in_or"}}</div>