refactor: replace legacy tw-flex utility classes with flex-text-block/inline (#36778)

## Summary

Replace combinations of `tw-flex tw-items-center` (with optional
`tw-gap-*`) with semantic `flex-text-block` or `flex-text-inline`
classes across 15 template files.

This follows the refactoring direction outlined in #35015 ("Refactor
legacy `tw-flex tw-items-center tw-gap-xx` to `flex-text-block` or
`flex-text-inline`").

## Changes

### Replacement rules applied:
- `tw-flex tw-items-center tw-gap-2` → `flex-text-block` (both have
`gap: 0.5rem`)
- `tw-flex tw-items-center tw-gap-1` → `flex-text-inline` (both have
`gap: 0.25rem`)
- `tw-flex tw-items-center` (no explicit gap) → `flex-text-block` where
the element is block-level and children benefit from the default gap
- `tw-flex tw-items-center` (inline context, e.g. `<a>`, `<span>`) →
`flex-text-inline`

### Files modified (15):
- `templates/admin/config.tmpl` — config page dt elements
- `templates/admin/repo/unadopted.tmpl` — unadopted repo list items
- `templates/base/head_navbar.tmpl` — active stopwatch popup
- `templates/org/header.tmpl` — org header action buttons
- `templates/org/home.tmpl` — member/team count links
- `templates/org/settings/labels.tmpl` — labels page header
- `templates/repo/branch/list.tmpl` — branch list header
- `templates/repo/commits_table.tmpl` — commits table header
- `templates/repo/diff/box.tmpl` — diff detail box
- `templates/repo/diff/new_review.tmpl` — review form header
- `templates/repo/issue/card.tmpl` — issue card unpin button
- `templates/repo/issue/view_content/attachments.tmpl` — attachment file
size
- `templates/repo/migrate/migrate.tmpl` — migration service cards
- `templates/shared/user/org_profile_avatar.tmpl` — org profile header
- `templates/webhook/new.tmpl` — webhook type dropdown text

### What was NOT changed:
- Elements with `tw-justify-between` or `tw-justify-center` (these need
additional classes)
- Elements whose children use explicit margins (`tw-mr-*`, `tw-ml-*`)
that would conflict with the gap from flex-text classes
- Fomantic UI form elements with special layout requirements

## Notes
- This PR was created with AI assistance (Claude). All changes were
reviewed individually to ensure semantic correctness and zero unintended
visual changes.
- No functional changes — purely CSS class refactoring.

Closes: part of #35015

Signed-off-by: xiaox315 <xiaox315@users.noreply.github.com>
Co-authored-by: xiaox315 <xiaox315@users.noreply.github.com>

templates/admin/config.tmpl

@@ -223,7 +223,7 @@
 					<dt>{{ctx.Locale.Tr "admin.config.mailer_user"}}</dt>
 					<dd>{{if .Mailer.User}}{{.Mailer.User}}{{else}}(empty){{end}}</dd>
 					<div class="divider"></div>
-					<dt class="tw-py-1 tw-flex tw-items-center">{{ctx.Locale.Tr "admin.config.send_test_mail"}}</dt>
+					<dt class="flex-text-block tw-py-1">{{ctx.Locale.Tr "admin.config.send_test_mail"}}</dt>
 					<dd class="tw-py-0">
 						<form class="ui form ignore-dirty" action="{{AppSubUrl}}/-/admin/config/test_mail" method="post">
 							<div class="ui tiny input">
@@ -254,7 +254,7 @@
 					<dd>{{.CacheItemTTL}}</dd>
 				{{end}}
 				<div class="divider"></div>
-				<dt class="tw-py-1 tw-flex tw-items-center">{{ctx.Locale.Tr "admin.config.cache_test"}}</dt>
+				<dt class="flex-text-block tw-py-1">{{ctx.Locale.Tr "admin.config.cache_test"}}</dt>
 				<dd class="tw-py-0">
 					<form class="ui form ignore-dirty" action="{{AppSubUrl}}/-/admin/config/test_cache" method="post">
 						<button class="ui tiny primary button">{{ctx.Locale.Tr "test"}}</button>