fix(coralbricks): drop PDF input from GLM 5.3 Flash

[divyvasal]

#6795 added coralbricks/glm-5.3-flash-fp4 on top of the zhipuai/glm-5.3-flash baseline, which lists input = ["text", "image", "video", "pdf"]. The CoralBricks endpoint serves text, image and video for this model but not PDF, so this overrides [modalities] to match what it accepts.

Checked against the production endpoint on 2026-09-14:

input	request shape	result
image	Chat Completions image_url	200, correct answer
video	Chat Completions video_url	200, correct answer
PDF	Chat Completions file part	400
PDF	Messages document block	400
PDF	Responses input_file	200, but the file is not passed to the model

bun run validate passes. bun test shows the same 7 failures as a clean dev checkout, none touching this file.

cc @rekram1-node

🤖 Generated with Claude Code

[github-actions]

No actionable findings.

[divyvasal]

Update on the table above: the Responses input_file row now returns 400 as well. The gateway was silently dropping the part; that's fixed on the production endpoint as of today, so PDF input is rejected on every wire. No change to this PR.