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-sampler/src/config.rs

@@ -71,12 +71,12 @@ pub struct SamplerConfig {
     // Reasoning effort
     pub reasoning_effort: Option<ReasoningEffort>,
 
-    // Client identity
+    /// Client identity for the User-Agent header (`kigi/{version}` plus an
+    /// optional origin product). The old xAI proxy's identity headers
+    /// (`x-grok-client-identifier` / `-client-version` / `-deployment-id` /
+    /// `-user-id`) are gone — User-Agent and `extra_headers` are the only
+    /// identity signals on the wire.
     pub origin_client: Option<OriginClientInfo>,
-    pub client_identifier: Option<String>,
-    pub deployment_id: Option<String>,
-    pub user_id: Option<String>,
-    pub client_version: Option<String>,
 
     /// Optional hook invoked at every UNAUTHORIZED (401) response
     /// site. The sampler passes the bearer that was actually sent on
@@ -146,10 +146,6 @@ impl Default for SamplerConfig {
             idle_timeout_secs: None,
             reasoning_effort: None,
             origin_client: None,
-            client_identifier: None,
-            deployment_id: None,
-            user_id: None,
-            client_version: None,
             attribution_callback: None,
             bearer_resolver: None,
             supports_backend_search: false,