fix(auth): align the social-login surfaces with the reference theme

The "other login methods" block drifted from zibll on three axes. Gitee was
mapped to fa-code-branch because FA5 Free ships no Gitee brand glyph, so the
button showed a generic branch icon; Google showed the monochrome FA glyph
instead of the reference's multi-colour mark. The modal also printed an
implicit agreement line under the social buttons, which the reference guest
card does not have. And the top-nav user popover built its own
.social-login-divider / .oauth-row / .oauth-btn markup and then wrapped that
in a second separator and .social_loginbar, so the block rendered nested and
unlike the reference.

aksrt_brand_icon() now routes zibsvg-/customsvg- values through the shared
icon renderer, and the brand map resolves gitee to zibsvg-gitee and google to
zibsvg-google-color. Both sprite keys already exist in the runtime symbol
sheet, which the loader pulls in on every frontend page. Because
get_auth_providers_data() and binding_row() both go through
aksrt_brand_icon(), one map change fixes the icon on the modal, the user card,
the top-nav popover, the user-center binding list and the profile social
links.

render_social_buttons() is rewritten to the reference shape: an optional
.social-separator, a .social_loginbar, and one .social-login-item <type>
toggle-radius anchor per enabled provider with rel="nofollow" and a
"<label>登录" title. oauth_button_lg switches to the button-lg variant with a
label, and the WeChat entry carries qrcode-signin so auth.js opens the QR
panel instead of navigating, matching the reference. The navbar and the link
apply modal now append the block verbatim instead of re-wrapping it, and the
user-card loop adopts the same item attributes. The retired
.social-login-divider / .oauth-row / .oauth-btn rules are dropped from
base-1.css, and the binding-list icon rule gains an svg selector so the
sprite icons keep the 22px the FA glyphs had.

Verification: node --test across widget-system, navigation, admin,
asset-ledger, dev, front-submit and visual (613 tests), plus php -l on every
changed PHP file. Extended the auth source contract with the agreement-line,
brand-icon and popover-structure cases, and pinned the user-card guest
markup.

tests/widget-system/user-card-runtime-contract.test.cjs

@@ -23,9 +23,13 @@ test('user and author widgets render the reference state contract', () => {
   assert.match(data.guest, /signup-loader ml10 but jb-yellow padding-lg/)
   assert.match(data.guest, /social-separator separator muted-3-color em09 mt20 mb20/)
   assert.match(data.guest, /social_loginbar/)
-  assert.match(data.guest, /class="social-login-item github"/)
-  assert.match(data.guest, /class="social-login-item qq" data-provider="clogin_qq"/)
+  assert.match(data.guest, /class="social-login-item github toggle-radius"/)
+  assert.match(data.guest, /class="social-login-item qq toggle-radius" data-provider="clogin_qq"/)
+  assert.match(data.guest, /title="GitHub登录"/)
   assert.doesNotMatch(data.guest, /aksrt-widget|aksrt-panel-wrap|user-card__auth-btns|oauth-row|oauth-btn/)
+  // The social-login area carries no agreement copy; the reference guest card
+  // only shows the separator, the .social_loginbar and the provider buttons.
+  assert.doesNotMatch(data.guest, /我已阅读并同意|使用社交账号登录即表示|注册即表示/)
 
   assert.match(data.guest_no_registration, /signin-loader but jb-blue padding-lg/)
   assert.doesNotMatch(data.guest_no_registration, /signup-loader/)