Fixes GitKraken AI model selection showing 'No models found'

[shoaib-fixes]

Fixes #4963

Description

When selecting the GitKraken AI provider in the Switch AI Provider/Model... picker, the model dropdown was always empty when selecting copilot as the provider. Tracked it down to GitKrakenProvider.getModels() — the whole method body was wrapped in a try/catch that silently returned [] on any error (auth failures, HTTP errors, bad responses). There was no way to tell whether models just didn't exist or something had actually gone wrong.

• Removes silent error swallowing in GitKrakenProvider.getModels() — errors now propagate so callers can handle them
• Checks for a valid auth token via getApiKey before making the API request, returning [] early if unauthenticated
• Passes the access token explicitly to getGkHeaders() instead of relying on the internal lookup that could throw AuthenticationRequiredError silently
• Adds a null guard on result.data to handle missing/null API response fields
• Removes a leftover debugger statement
• Catches getModels() errors in showAIModelPicker and shows 'Unable to load models' with the error description instead of the generic 'No models found'
• Adds a defensive try/catch in getOrUpdateModel around the getModels() call used to restore a previously configured model at startup

Screenshots showing model selection from copilot:

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