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/agent/subagent/handle_request.rs

@@ -708,7 +708,6 @@ pub(crate) async fn handle_subagent_request(
         api_key: effective_sampling_config.api_key.clone(),
         auth_type: inherited_auth_type,
         alpha_test_key: ctx.alpha_test_key.clone(),
-        client_version: effective_sampling_config.client_version.clone(),
     };
     kigi_log::unified_log::info(
         "subagent spawn credentials",
@@ -1020,9 +1019,6 @@ pub(crate) async fn handle_subagent_request(
             false,
             subagent_fs_watch,
             None,
-            None,
-            None,
-            None,
             false,
             false,
             std::sync::Arc::new(std::sync::atomic::AtomicBool::new(true)),
@@ -1057,7 +1053,6 @@ pub(crate) async fn handle_subagent_request(
             } else {
                 ctx.memory_config.clone()
             },
-            false,
             Default::default(),
             ctx.managed_mcp_state.clone(),
             None,