[WIP] BREAKING: New diff and streamlining of features

[olimorris]

Description

Ref: zed-industries/zed#43269

This PR will enable a more thorough diff experience in CodeCompanion, allowing for:

• Syntax highlighting for additions and deletions (current implementation allows for just additions)
• Hunk navigation
• Word level highlighting (similar to Zed's diff)
• Keymap instructions that move when you navigate hunks
• Unified diff across the builtin tools and ACP tools
• Integration testing with screenshots - making it easier to debug diff output

This PR will also see the removal of support for other diff providers as I seek to streamline CodeCompanion into 2026, keeping it simpler and leaner. Unfortunately this means a number of destructive changes:

1. No support for mini.diff and the builtin split provider
2. Replacement of the current inline provider
3. Removal of the superdiff feature and edit tracker

Regarding the latter, these are two very useful and complex features and my view is that they should exist as separate plugins to CodeCompanion.

Checklist

• I've read the contributing guidelines and have adhered to them in this PR
• I've run make all to ensure docs are generated, tests pass and StyLua has formatted my code
• (optional) I've added test coverage for this fix/feature
• (optional) I've updated the README and/or relevant docs pages

[cloudflare-workers-and-pages]

Deploying codecompanion with    Cloudflare Pages

Latest commit:	b414d75
Status:	✅  Deploy successful!
Preview URL:	https://83994da3.codecompanion.pages.dev
Branch Preview URL:	https://feat-new-diff.codecompanion.pages.dev

View logs