5.0.0 release TODO

[deathbeam]

• Change selection to context - refactor(select)!: remove selection API in favor of resources #1340
• Improve chat renderer - feat(chat): switch to treesitter based chat parsing #1394
• Improve diffing algorithm and generation - feat(diff): add experimental unified diff support, refactor handling #1392
• Switch to new prompt parser - feat(prompt): support custom Copilot instructions file #1467
• Move state tracking to chat window (source and sticky) - refactor!: move source/sticky logic to chat window #1469
• Add support for Responses API - gpt-5-codex is not accessible via the chat/completions endpoint #1442
• Improve provider interface so adding stuff like copilot enterprise isnt so annoying for users - wip: config #1349