Fix: Correct model ID for Gemini 3 Pro in GitHub provider

[I3eka]

Bug Fix

The model ID for Gemini 3 Pro in the GitHub Copilot (gh) provider was missing the -preview suffix, which caused requests to this model to fail.

Changes

• Updated the ID for Gemini 3 Pro from gemini-3-pro to gemini-3-pro-preview.

Verification

I confirmed locally that the model does not work with the old ID but functions correctly after this change.

[Copilot]

Pull request overview

Fixes GitHub Copilot (gh) provider’s Gemini 3 Pro model identifier so requests don’t fail due to a missing -preview suffix.

Changes:

• Updated gh Gemini 3 Pro model id from gemini-3-pro to gemini-3-pro-preview.

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[Copilot]

The display name here is inconsistent with the actual model ID and with other entries in this same file (e.g., gc and gemini both label gemini-3-pro-preview as “Gemini 3 Pro Preview”). Keeping the name as “Gemini 3 Pro” may confuse users who expect the stable/non-preview variant; consider renaming to “Gemini 3 Pro Preview” for consistency/clarity.

Suggested change

	{ id: "gemini-3-pro-preview", name: "Gemini 3 Pro" },
	{ id: "gemini-3-pro-preview", name: "Gemini 3 Pro Preview" },

[Copilot]

Changing the gh model ID from gemini-3-pro to gemini-3-pro-preview will leave other mappings out of sync: src/shared/constants/pricing.js still defines GitHub Copilot pricing under the old key (gh["gemini-3-pro"]), and README usage examples still reference gh/gemini-3-pro. This will likely result in missing/incorrect pricing display for this model and outdated docs unless those references are updated as part of this PR.

Suggested change

	{ id: "gemini-3-pro-preview", name: "Gemini 3 Pro" },
	{ id: "gemini-3-pro", name: "Gemini 3 Pro" },