fix(zai): add missing glm-4.6v-flash provider model

[pc-gs]

Issue for this PR

Fixes #1470

Type of change

• Bug fix

What does this PR do?

providers/zhipuai/models/glm-4.6v-flash.toml is a symlink to ../../zai/models/glm-4.6v-flash.toml, but that Z.AI provider file was missing, so the catalog entry was broken.

This adds providers/zai/models/glm-4.6v-flash.toml as an override-only provider model:

• base_model = "zhipuai/glm-4.6v-flash" (lab metadata already exists at models/zhipuai/glm-4.6v-flash.toml)
• [[reasoning_options]] toggle (same pattern as peer Z.AI GLM flash / vision entries)
• Free [cost] shaped like providers/zai/models/glm-4.5-flash.toml

The existing zhipuai symlink is left in place and now resolves.

How did you verify your code works?

• Confirmed the zhipuai path is still a symlink to the missing zai file on dev
• Confirmed models/zhipuai/glm-4.6v-flash.toml already exists
• bun validate passes after adding the provider file
• Symlink resolves to the new file locally

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

No actionable findings.