F3: Kimi inference pipeline + full grok cloud-surface excision

Sampler / inference (PRD F3):
- kimi_compat.rs: single adaptation point for the Kimi chat/completions
  dialect (thinking-field mapping, model_id stripping, empty-content
  tool-call message fix, stream_options.include_usage), with kimi-cli
  source citations
- Rate-limit handling reworked for Kimi/Moonshot semantics; UA kigi/{version}
- /models replaces the xAI models-v2 endpoint everywhere; idle model
  refresh carries X-Msh-* device headers only (X-XAI-Token-Auth and
  x-grok-client-mode/CLIENT_MODE_HEADER machinery deleted)

Cloud-surface excision (PRD §5, zero-egress):
- remote/ conversations lane, cli-chat-proxy-types crate, prod/ dir,
  share command, credit bar: deleted (single local session lane;
  paginate() replaces merge_and_paginate)
- Subscription/tier gate stack deleted end-to-end: AppView
  gate/tier/team/ZDR fields, app/subscription.rs watch loop,
  dispatch/billing.rs paywall + SuperGrok upsell, free-usage-exhausted
  chain, tier-restricted commands, GateInfo, RemoteSettings gate fields,
  SettingsUpdateNotification gate fields
- /privacy + coding-data-sharing setting deleted (backed by a dead xAI
  RPC; Kigi is zero-egress — nothing to share or retain remotely)

Auth UX correctness (user-reported):
- Device-flow fixtures now mirror the live Kimi payload shape
  (https://www.kimi.com/code/authorize_device?user_code=..., verified
  against auth.kimi.com); the fabricated auth.kimi.com/device?code=...
  URLs are gone
- open_browser_detached is a no-op under cfg(test): unit tests drove
  wiremock fixture URLs into the real browser (root cause of the
  "garbage mock link" ABCD-1234 tabs)
- Welcome/pager-minimal rebrand: Grok Build -> Kigi, grok.com ->
  kimi.com, "Sign in to Grok" -> "Sign in to Kimi"

crates/codegen/kigi-shell/src/auth/kimi_oauth.rs

@@ -359,11 +359,11 @@ mod tests {
                 "client_id={KIMI_CODE_CLIENT_ID}"
             )))
             .respond_with(ResponseTemplate::new(200).set_body_json(serde_json::json!({
-                "user_code": "ABCD-1234",
+                "user_code": "WXYZ-6789",
                 "device_code": "dev-code-1",
-                "verification_uri": "https://auth.kimi.com/device",
-                "verification_uri_complete": "https://auth.kimi.com/device?code=ABCD-1234",
-                "expires_in": 600,
+                "verification_uri": "https://www.kimi.com/code/authorize_device",
+                "verification_uri_complete": "https://www.kimi.com/code/authorize_device?user_code=WXYZ-6789",
+                "expires_in": 1800,
                 "interval": 7,
             })))
             .expect(1)
@@ -371,13 +371,13 @@ mod tests {
             .await;
 
         let auth = request_device_authorization(&server.uri()).await.unwrap();
-        assert_eq!(auth.user_code, "ABCD-1234");
+        assert_eq!(auth.user_code, "WXYZ-6789");
         assert_eq!(auth.device_code, "dev-code-1");
         assert_eq!(auth.interval, 7);
-        assert_eq!(auth.expires_in, Some(600));
+        assert_eq!(auth.expires_in, Some(1800));
         assert_eq!(
             auth.verification_uri_complete,
-            "https://auth.kimi.com/device?code=ABCD-1234"
+            "https://www.kimi.com/code/authorize_device?user_code=WXYZ-6789"
         );
     }
 
@@ -392,7 +392,7 @@ mod tests {
             .respond_with(ResponseTemplate::new(200).set_body_json(serde_json::json!({
                 "user_code": "AAAA",
                 "device_code": "d",
-                "verification_uri_complete": "https://auth.kimi.com/device?code=AAAA",
+                "verification_uri_complete": "https://www.kimi.com/code/authorize_device?user_code=AAAA",
                 "interval": 5,
             })))
             .expect(1)
@@ -409,7 +409,7 @@ mod tests {
             .respond_with(ResponseTemplate::new(200).set_body_json(serde_json::json!({
                 "user_code": "AAAA",
                 "device_code": "d",
-                "verification_uri_complete": "https://auth.kimi.com/device?code=AAAA",
+                "verification_uri_complete": "https://www.kimi.com/code/authorize_device?user_code=AAAA",
             })))
             .mount(&server)
             .await;