Promotes AI features from experimental to preview status

[axosoft-ramint]

Changes

• Updates feature labels from "Experimental" to "Preview" across all AI commit generation and rebase functionality
• Removes experimental configuration gates that previously required explicit enablement of the two AI features
• Adds one-time confirmation dialogs to inform users about the impact of AI operations before execution (closes Add modal to introduce the commands for generate commits and generate rebase #4367)

The changes make AI commit generation and rebase features more accessible while ensuring users understand the implications of these operations through improved messaging and confirmation workflows.

[axosoft-ramint]

As a fun side-fact, the commits in this PR were generated with the "generate commits with AI" command, and its title and description were generated with the "create PR with AI" command.