feat(models): add Kimi K3 to Claude adapter

[tatoalo]

Problem

Kimi K3 🚀

[trunk-io]

😎 Merged directly without going through the merge queue, as the queue was empty and the PR was up to date with the target branch - details.

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 82a1d15.}

[posthog]

👋 Visual changes detected for this PR.

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[greptile-apps]

Prompt To Fix All With AI

### Issue 1
packages/agent/src/adapters/base-acp-agent.ts:160
**Modal compatibility check drops Kimi**

When gateway model discovery fails or temporarily omits `moonshotai/kimi-k3`, the ID-only compatibility guard does not recognize the newly supported Modal model and replaces it with `claude-opus-4-8`, causing the session to run a different model than the user selected.

### Issue 2
packages/ui/src/features/sessions/modelOptionFilters.ts:43-49
**Hidden Kimi remains selected**

When the Kimi flag is disabled while `moonshotai/kimi-k3` is the current value, this filter removes only the menu option and preserves `currentValue`, so task creation still submits the hidden model and active sessions display its raw ID without a matching selected item.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "chore(models): rename Kimi rollout flag" | Re-trigger Greptile}

[github-actions]

Contained, flag-gated feature adding a new model option; both Greptile P1 concerns (Modal ID-fallback recognition, stale currentValue when Kimi is hidden) are directly fixed in the current diff with accompanying unit tests, and the change doesn't touch billing, auth, migrations, dependencies, or CI.

• Author wrote 0% of the modified lines and has 127 merged PRs in these paths (familiarity MODERATE).
• 👍 on the PR from greptile-apps[bot].

Gate mechanics and policy version

Gate		Result
prerequisites	✓	all clear
deny-list	✓	no deny categories matched
size	✓	147L, 9F substantive, 179L/11F incl. docs/generated/snapshots — within ceiling
tier	✓	T1-agent / T1c-medium (179L, 11F, single-area, feat)
stamphog 2.0.0b3		.stamphog/policy.yml @ 9ddb5f3 · reviewed head 82a1d15