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-tui/src/app/dispatch/tests/session/lifecycle.rs

@@ -50,7 +50,7 @@ fn session_created_sets_session_id() {
         }),
         &mut app,
     );
-    assert_eq!(effects.len(), 5);
+    assert_eq!(effects.len(), 4);
     assert!(
         matches!(& effects[0], Effect::FetchPromptHistory { session_id, .. } if
         session_id == "new-session-123")
@@ -60,11 +60,7 @@ fn session_created_sets_session_id() {
         &effects[2],
         Effect::RefreshAvailableCommands { .. }
     ));
-    assert!(matches!(
-        &effects[3],
-        Effect::FetchBilling { silent: true, .. }
-    ));
-    assert!(matches!(&effects[4], Effect::RegisterActiveSession { .. }));
+    assert!(matches!(&effects[3], Effect::RegisterActiveSession { .. }));
     assert_eq!(
         app.agents[&id]
             .session
@@ -198,11 +194,6 @@ fn worktree_session_created_sets_session_and_cwd() {
             .iter()
             .any(|e| matches!(e, Effect::FetchSessionAgentName { .. }))
     );
-    assert!(
-        effects
-            .iter()
-            .any(|e| matches!(e, Effect::FetchBilling { silent: true, .. }))
-    );
     assert!(
         effects
             .iter()