Switch from callbacks to webhooks for repos

[ZIJ]

🧠 AI Assistance Disclosure Policy

Important

Inspired by ghostty.
If you used any AI assistance while contributing to Digger, you must disclose it in this PR.

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✅ AI Disclosure Checklist

• I understand that all AI assistance must be disclosed.
• I did not use AI tools in this contribution.
• I used AI tools and have disclosed details below.

Details (if applicable):

used codex heavily

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[motatoes]

in case its first instllation the link will only be created on the callback and here we depend on it so we need a retry mechanism incase the webhook arrives before the callback over here. We can retry like 3 to 5 times to fetch the link and if not we call it a failure

[ZIJ]

addressed

[motatoes]

In the callback function there is this part on top

	if !codeExists || len(codeParams) == 0 {
		slog.Error("There was no code in the url query parameters")
		c.String(http.StatusBadRequest, "could not find the code query parameter for github app")
		return
	}

However since moving updates to webhook a missing code parameter is no longer considered an error (the update will happen in the webhook) so that step should return a success message