feat(models): add GLM-5.1 to the Z.ai GLM Coding Plan (#1650)

## Summary

- Adds GLM-5.1 as a new model in the Z.ai Coding Plan (`zai-coding`
provider), placed above GLM-5 with the `recommended` flag,
`context_length: 204800`, and `max_completion_tokens: 131072` (matching
GLM-5 specs per the [Z.ai docs](https://docs.z.ai/devpack/using5.1)).
- Registers `z-ai/glm-5.1` in `preferredModels`, `KILOCODE_CATALOG_IDS`
(for older OpenClaw builds), `forbidden-free-models`, and the legacy
`modelstats` route.

## Verification

- Reviewed all changed files manually; all new entries follow the exact
same TypeScript shapes as existing GLM-5 entries.
- `pnpm typecheck` could not run due to missing environment dependencies
(`tsgo` not found), which is a pre-existing environment issue unrelated
to this change.

## Visual Changes

N/A

## Reviewer Notes

GLM-5.1 has identical context/token limits to GLM-5 (204800 / 131072).
The description is derived from GLM-5's description updated to reference
5.1 as the latest iteration, per the instructions to copy GLM-5. The
`modelstats` cost figures are copied from GLM-5 as a placeholder since
no separate pricing data is available for 5.1 yet (this route serves
legacy clients with mock data).

Author: chrarnoldus

src/lib/providers/coding-plans/coding-plan-definitions.ts

@@ -98,6 +98,15 @@ export default [
         context_length: 202752,
         max_completion_tokens: 131072,
       },
+      {
+        id: 'glm-5.1',
+        name: 'GLM-5.1',
+        description:
+          "GLM-5.1 is Z.ai's latest iteration of the flagship open-source foundation model engineered for complex systems design and long-horizon agent workflows. Built for expert developers, it delivers production-grade performance on large-scale programming tasks, rivaling leading closed-source models. With advanced agentic planning, deep backend reasoning, and iterative self-correction, GLM-5.1 moves beyond code generation to full-system construction and autonomous execution.",
+        flags: ['recommended'],
+        context_length: 204800,
+        max_completion_tokens: 131072,
+      },
       {
         id: 'glm-5',
         name: 'GLM-5',