feat(models): add September 2026 models + Z.ai (GLM) provider

- Anthropic: claude-opus-5-5 (default), claude-fable-5-1
- OpenAI: gpt-6-astra / gpt-6-sol / gpt-6-luna
- Google: gemini-3.8-flash
- Qwen: qwen3.8-max, qwen3.8-omni-flash
- new provider zai (Z.ai / GLM): glm-5.3, glm-5.3-flashx, glm-4.6
- refresh opencode + openrouter curated lists (glm-5.3, deepseek-v4.1, qwen3.8-max, opus-5-5)
- web console PROVIDERS mirror synced; also fixes stale xai list (adds grok-4.7)
- routing is by provider, not model id, so new ids pass through unchanged
- README badge 18 -> 19 providers; 390 tests passing

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

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   <img src="https://img.shields.io/badge/Harness-Rust%20%7C%20tokio-e6b673?style=flat-square">
   <img src="https://img.shields.io/badge/License-MIT-green?style=flat-square">
   <img src="https://img.shields.io/badge/MD%20Agents-458-red?style=flat-square">
-  <img src="https://img.shields.io/badge/Models-18%20providers-success?style=flat-square">
+  <img src="https://img.shields.io/badge/Models-19%20providers-success?style=flat-square">
   <img src="https://img.shields.io/badge/Modes-Black%20%7C%20White%20%7C%20Grey%20%7C%20Host%20%7C%20AI%20%7C%20Mobile%20%7C%20Container-9cf?style=flat-square">
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