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-config/src/signed_policy/tests.rs

@@ -956,3 +956,28 @@ fn rotation_selects_the_trusted_key_by_signed_key_id() {
         Err(SigError::SignatureMismatch)
     );
 }
+
+/// The version field round-trips, and a pre-versioned payload (no `version`
+/// key) defaults to 0 — old sidecars keep parsing.
+#[test]
+fn signed_payload_version_round_trips_and_defaults() {
+    let versioned = SignedPayload {
+        version: SIGNED_PAYLOAD_VERSION,
+        deployment_id: None,
+        team_id: Some("team-007".into()),
+        managed_config: None,
+        requirements: None,
+        fail_closed: false,
+        expires_at: 4_000_000_000,
+        key_id: "v1".into(),
+    };
+    let json = serde_json::to_string(&versioned).unwrap();
+    assert_eq!(
+        serde_json::from_str::<SignedPayload>(&json).unwrap(),
+        versioned
+    );
+
+    let legacy: SignedPayload =
+        serde_json::from_str(r#"{"expires_at": 1, "key_id": "v1"}"#).unwrap();
+    assert_eq!(legacy.version, 0, "pre-versioned payloads default to 0");
+}