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/views/agent.rs

@@ -889,7 +889,6 @@ pub fn build_hints(
     has_queued_follow_up: bool,
     selected_is_user_prompt: bool,
     selected_is_agent_message: bool,
-    selected_is_credit_limit: bool,
     shift_enter_unavailable: bool,
     scrollback_search: Option<&ScrollbackSearchState>,
 ) -> Vec<HintItem> {
@@ -1029,19 +1028,12 @@ pub fn build_hints(
             let mut hints = Vec::new();
             let nothing_special = !selected_is_agent_message
                 && !selected_is_user_prompt
-                && !selected_is_credit_limit
                 && fold_label.is_none()
                 && group_header_label.is_none()
                 && !selected_supports_fullscreen;
             if nothing_special {
                 hints.push(space_prompt_hint());
             }
-            if selected_is_credit_limit {
-                if let Some(key) = registry.key_for(ActionId::OpenBlockViewer) {
-                    hints.push(HintItem::new(key, "open"));
-                }
-                hints.push(space_prompt_hint());
-            }
             if selected_is_agent_message {
                 if vim_mode
                     && selected_supports_copy
@@ -1217,7 +1209,6 @@ mod tests {
             selected_is_user_prompt,
             selected_is_agent_message,
             false,
-            false,
             None,
         )
     }
@@ -1249,7 +1240,6 @@ mod tests {
             false,
             false,
             false,
-            false,
             None,
         );
         let labels: Vec<&str> = hints.iter().map(|h| h.label.as_ref()).collect();
@@ -1413,7 +1403,6 @@ mod tests {
             false,
             false,
             false,
-            false,
             Some(&search),
         )
     }
@@ -1516,7 +1505,6 @@ mod tests {
             false,
             false,
             false,
-            false,
             None,
         );
         assert!(
@@ -1559,7 +1547,6 @@ mod tests {
             false,
             false,
             false,
-            false,
             shift_enter_unavailable,
             None,
         )
@@ -1619,7 +1606,6 @@ mod tests {
                 false,
                 false,
                 false,
-                false,
                 None,
             );
             let labels: Vec<&str> = hints.iter().map(|h| h.label.as_ref()).collect();