feat(providers): add Z.AI coding plan (global + China)

Providers 17-18 (20th & 21st registry variants), sourced authoritatively
from Pi (earendil-works/pi), the open-source agent whose provider list is
being mirrored. Pi's zai.ts / zai-coding-cn.ts use plain openAICompletionsApi
(NO special thinking dialect — overturns the matrix's 'thinking:{type} → new
dialect' concern), so Kigi maps them to Passthrough. Global: api.z.ai/api/
coding/paas/v4, ZAI_API_KEY, models.dev zai-coding-plan. China (Zhipu
BigModel): open.bigmodel.cn/api/coding/paas/v4, ZAI_CODING_CN_API_KEY,
models.dev zhipuai-coding-plan. Both Bearer + OpenAI listing + ChatCompletions
+ restrict_to_enriched; /models is auth-gated → validator.

id-match is PROVEN (not just assumed like Qwen): Pi's static model ids
[glm-4.5-air, glm-4.7, glm-5-turbo, glm-5.1, glm-5.2, glm-5v-turbo] are
byte-identical to the models.dev zai-coding-plan keys, all tool_call=true, so
restrict keeps every model with no silent-empty risk. Review found no defects.
GLM thinking is not lost (reasoning_content is parsed regardless of dialect).

Tests: e2e proves enrichment-supplied context + non-vacuous restrict (a
non-enriched wire model is dropped) + Passthrough; both variants' validation
tests hit /models and assert the per-variant console host (z.ai vs
open.bigmodel.cn). Registry at 21; picker 22 rows.

Also fixes the welcome login-picker test for the now-taller menu (renders at
a taller viewport to verify content coverage) and logs the real menu-overflow
UX debt: the picker clips rows past the fold with no scroll (q/l shortcuts
still work; only shown when unauthenticated) — deferred to its own cycle.

crates/codegen/kigi-tui/src/app/app_view.rs

@@ -6894,7 +6894,7 @@ pub(crate) mod tests {
     #[test]
     fn pending_menu_items_lists_interactive_methods_plus_quit() {
         let items = pending_menu_items(&fresh_user_auth_methods(), None);
-        assert_eq!(items.len(), 20, "19 login rows + Quit, got {items:?}");
+        assert_eq!(items.len(), 22, "21 login rows + Quit, got {items:?}");
         assert!(
             matches!(&items[0], PendingMenuItem::Login { label } if label == "Kimi Code (OAuth)"),
             "row 0 must be the OAuth login, got {:?}",
@@ -7027,7 +7027,21 @@ pub(crate) mod tests {
                 label: "Kimi For Coding (API key)".into(),
             }
         );
-        assert_eq!(items[19], PendingMenuItem::Quit);
+        assert_eq!(
+            items[19],
+            PendingMenuItem::ApiKey {
+                target: PlatformLogin(kigi_shell::models::PlatformId::Zai),
+                label: "Z.AI (API key)".into(),
+            }
+        );
+        assert_eq!(
+            items[20],
+            PendingMenuItem::ApiKey {
+                target: PlatformLogin(kigi_shell::models::PlatformId::ZaiCodingCn),
+                label: "Z.AI Coding China (API key)".into(),
+            }
+        );
+        assert_eq!(items[21], PendingMenuItem::Quit);
         // The non-interactive methods must never appear as rows.
         let byok = kigi_shell::agent::auth_method::build_auth_methods(
             kigi_shell::agent::auth_method::AuthMethodsBuildInputs {
@@ -7038,7 +7052,7 @@ pub(crate) mod tests {
         );
         assert_eq!(
             pending_menu_items(&byok.methods, None).len(),
-            20,
+            22,
             "xai.api_key / cached_token must not add rows"
         );
     }