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/views/welcome/mod.rs

@@ -2070,7 +2070,16 @@ mod tests {
     }
 
     fn render_done_text(params: &WelcomeRenderParams<'_>) -> String {
-        let area = Rect::new(0, 0, 100, 40);
+        render_done_text_h(params, 40)
+    }
+
+    /// Render at an explicit height. The login picker lists one row per
+    /// advertised platform; with ~20 API-key providers the menu no longer
+    /// fits a 40-row viewport, so the full-menu content test needs more rows
+    /// to verify every label renders. (On-terminal, rows past the fold are
+    /// clipped — the `q`/`l` shortcuts still work; see the menu-scroll debt.)
+    fn render_done_text_h(params: &WelcomeRenderParams<'_>, height: u16) -> String {
+        let area = Rect::new(0, 0, 100, height);
         let mut buf = Buffer::empty(area);
         let mut prompt = PromptWidget::new();
         let mut picker = PickerState::default();
@@ -2093,7 +2102,9 @@ mod tests {
         let trust = TrustState::Done;
         let mut params = render_params(&auth, &trust, None);
         params.auth_methods = &built.methods;
-        let text = render_done_text(&params);
+        // Tall viewport so every advertised login row renders (the picker now
+        // lists ~20 platforms); this asserts content coverage, not fit.
+        let text = render_done_text_h(&params, 72);
         assert!(text.contains("Kimi Code (OAuth)"), "{text}");
         assert!(
             text.contains("Moonshot Open Platform (API key \u{b7} moonshot.cn)"),