[ChristopherPHolder]

What and why

Closes #131.

Every folder in apps/bot/src now has an index.ts that is its interface (#133, #134, #135), but nothing stopped code from reaching past it into a folder's internals. Over time the seams would wear away.

• A no-restricted-imports rule for apps/bot/src/** in the root vite.config.ts. A file may import siblings in its own folder, and other folders, parent or child, only through their index.ts. Anything deeper fails lint, with a message saying to use the folder's index.ts.
• recording/audio/ gets its own index.ts, so recording/ uses its audio pieces through an interface too.
• Tests and scripts aren't covered by the rule, so they can still test and use the internals.
• CONTRIBUTING.md describes the layout and the rule.

How I tested it

• I added a throwaway file in recording/ importing ../slack/BotPosts.ts, ./audio/ClipCutter.ts and ../office/index.ts. The first two failed with the rule's message, and the index.ts import passed.
• pnpm vp run ci passes, so the bot's code already keeps to the rule.

Checklist

• vp run ci passes
• Tests cover the change (the lint run is the test)
• Docs updated if what gets posted, the configuration, the Console or the deploy changed (CONTRIBUTING.md)
• New environment variables are wired through (none)
• Ready to ship: merging this deploys it to production