fix: replace broken extends with concrete glm-4.6v-flash def

zhipuai/glm-4.6v-flash.toml is a symlink to zai/models/glm-4.6v-flash.toml
which does not exist, causing validate to fail with 'Unable to resolve
extends.from'. Inline the concrete definition instead.

Author: smakosh

providers/llmgateway/models/glm-4.6v-flash.toml

@@ -1,2 +1,23 @@
-[extends]
-from = "zhipuai/glm-4.6v-flash"
+name = "GLM-4.6V Flash"
+family = "glm"
+release_date = "2025-12-08"
+last_updated = "2025-12-08"
+attachment = true
+reasoning = true
+temperature = true
+tool_call = true
+structured_output = true
+open_weights = true
+status = "beta"
+
+[cost]
+input = 0.00
+output = 0.00
+
+[limit]
+context = 128_000
+output = 16_000
+
+[modalities]
+input = ["text", "image"]
+output = ["text"]