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/fork.rs

@@ -3,9 +3,7 @@
 //! Forks a saved session to a new working directory with a new session ID.
 //! This creates new session files but does not start the session.
 
-use crate::remote::BackendClient;
-const FORK_LOG: &str = "xai_fork";
-use crate::session::export::ExportedMetadata;
+const FORK_LOG: &str = "kigi_fork";
 use crate::session::info::Info;
 use crate::session::storage::{CopySessionOptions, JsonlStorageAdapter};
 use crate::util::kigi_home::kigi_home;
@@ -62,11 +60,7 @@ fn generate_fork_session_id(_source_id: &str) -> String {
 }
 
 /// Fork a saved session to a new working directory.
-pub async fn fork_session(
-    request: ForkSessionRequest,
-    agent_id: &str,
-    auth_manager: Option<std::sync::Arc<crate::auth::AuthManager>>,
-) -> io::Result<ForkSessionResponse> {
+pub async fn fork_session(request: ForkSessionRequest) -> io::Result<ForkSessionResponse> {
     let t0 = std::time::Instant::now();
 
     let root_dir = kigi_home();
@@ -114,32 +108,6 @@ pub async fn fork_session(
 
     let copy_ms = t0.elapsed().as_millis() as u64;
 
-    // Writeback session to backend (fire-and-forget).
-    // This is telemetry-grade: the local fork works without it. All fork
-    // state lives locally (session files on disk), and the caller does not
-    // depend on synchronous backend registration. The backend eventually
-    // learns about the session when the background task completes.
-    // Spawning removes the network round-trip (~200-400ms) from the
-    // critical path.
-    if let Some(am) = auth_manager {
-        let sid = new_session_id.clone();
-        let cwd = request.new_cwd.clone();
-        let parent = request.source_session_id.clone();
-        let model = request.new_model_id.clone();
-        let aid = agent_id.to_string();
-        tokio::spawn(async move {
-            if let Err(e) =
-                sync_forked_session_to_backend(&sid, &cwd, parent, model, &aid, am).await
-            {
-                tracing::warn!(
-                    session_id = %sid,
-                    error = %e,
-                    "Failed to register forked session with backend (background)"
-                );
-            }
-        });
-    }
-
     let total_ms = t0.elapsed().as_millis() as u64;
     tracing::info!(
         target: FORK_LOG,
@@ -149,7 +117,7 @@ pub async fn fork_session(
         total_ms,
         chat_copied = result.chat_messages_copied,
         updates_copied = result.updates_copied,
-        "FORK_COPY: session data copied (backend sync spawned in background)"
+        "FORK_COPY: session data copied"
     );
 
     Ok(ForkSessionResponse {
@@ -163,43 +131,6 @@ pub async fn fork_session(
     })
 }
 
-/// Sync a forked session to the backend (for writeback mode).
-async fn sync_forked_session_to_backend(
-    session_id: &str,
-    cwd: &str,
-    parent_session_id: String,
-    model_id: Option<String>,
-    agent_id: &str,
-    auth_manager: std::sync::Arc<crate::auth::AuthManager>,
-) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
-    let client = BackendClient::new().with_auth_manager(auth_manager);
-    let metadata = ExportedMetadata {
-        title: None, // Will be generated later when session runs
-        cwd: cwd.to_string(),
-        model_id,
-        created_at: Some(chrono::Utc::now().to_rfc3339()),
-        updated_at: Some(chrono::Utc::now().to_rfc3339()),
-        total_messages: Some(0),
-        parent_session_id: Some(parent_session_id),
-        session_kind: None,
-        subagent_type: None,
-        subagent_persona: None,
-        subagent_role: None,
-        fork_context_source: None,
-        subagent_depth: None,
-    };
-
-    client
-        .upsert_session(session_id, &metadata, agent_id)
-        .await?;
-    tracing::info!(
-        session_id = %session_id,
-        "Forked session registered with backend"
-    );
-
-    Ok(())
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;