Fix: incorrect Gemini 3 Flash ID for GitHub provider

[I3eka]

Bug Fix

The model ID for Gemini 3 Flash in the GitHub Copilot (gh) provider was incorrect (gemini-3-flash), causing it to fail. The correct ID requires the -preview suffix.

Changes

• Updated the ID from gemini-3-flash to gemini-3-flash-preview in the gh provider list.

Verification

I tested this locally.

• Before: The model failed to load with the old ID.
• After: The model works correctly with the updated ID.

[Copilot]

Pull request overview

Fixes GitHub Copilot (gh) provider model selection by correcting the Gemini 3 Flash model ID to the required -preview variant so the model can load successfully.

Changes:

• Update gh provider model ID from gemini-3-flash to gemini-3-flash-preview.

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[Copilot]

gh now lists gemini-3-flash-preview, but DEFAULT_PRICING.gh (and any other pricing/model lookup tables keyed by model ID) still use gemini-3-flash. This will make cost calculation fall back to $0 for this model. Update the corresponding pricing key (or provide an alias/mapping) so the new model ID has pricing data.

Suggested change

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

[Copilot]

The display name Gemini 3 Flash no longer matches the selected model ID gemini-3-flash-preview. Consider renaming this entry to include Preview (to match the gc provider’s naming) so users can distinguish preview vs non-preview models in the UI/logs.

Suggested change

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

[I3eka]

@decolua i fix version conflict