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/session/compaction.rs

@@ -7,7 +7,7 @@
 //! lives alongside the primary one in `acp_session.rs`.
 use super::SessionActor;
 use super::is_project_instructions;
-use crate::remote::DEFAULT_CONTEXT_WINDOW;
+use crate::agent::models_fetch::DEFAULT_CONTEXT_WINDOW;
 use crate::session::compaction_config::{
     AsyncCompactionCache, SUPPRESS_NONE, SUPPRESS_STICKY, SUPPRESS_TURN, SUPPRESS_UNTIL_SUCCESS,
 };
@@ -2242,7 +2242,6 @@ mod inline_auto_compact_flow_tests {
             client_identifier: None,
             origin_client: None,
             feedback_manager: Arc::new(FeedbackManager::local_only("test-session")),
-            sync_loop_cancel: None,
             agent: std::cell::RefCell::new(test_agent_default().await),
             last_reported_branch: std::sync::Arc::new(parking_lot::Mutex::new(None)),
             git_head_enabled: false,