docs: eslint (#8269)

docs/eslint.md

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+# ESLint in Plane - How It Works
+
+We've recently upgraded our ESLint setup to use **typed linting** with a **single root-level configuration**. This means faster lint runs and simpler config management across the entire monorepo.
+
+## Key Changes
+
+1. **Single Root Config** - Instead of individual `eslint.config.mjs` files in every package, we now have one config at the repo root that handles all packages and apps
+2. **Typed Linting Enabled** - ESLint now uses TypeScript's type information for more powerful checks (catching things like floating promises, unsafe any usage, etc.)
+3. **ESLint Flat Config** - We're using ESLint v9's new flat config format
+
+## How to Run ESLint
+
+From the root of the repo:
+
+```bash
+# Check for lint errors
+pnpm check:lint
+
+# Auto-fix lint errors
+pnpm fix:lint
+```
+
+## VS Code Integration
+
+ESLint should work automatically in VS Code. The extension will:
+
+- Show inline errors/warnings as you type
+- Use the root `eslint.config.mjs` for all files in the monorepo
+
+**Tip:** Make sure you have the [ESLint extension](https://marketplace.visualstudio.com/items?itemName=dbaeumer.vscode-eslint) installed.
+
+## What Gets Linted
+
+The config applies to all TypeScript and JavaScript files across:
+
+- `apps/web`, `apps/admin`, `apps/space`, `apps/live`
+- All packages in `packages/`
+
+**Ignored paths:**
+
+- `node_modules/`, `dist/`, `build/`, `.next/`, `.turbo/`
+- Config files (`*.config.{js,mjs,cjs,ts}`)
+- Public folders
+
+## Rules Overview
+
+We're enforcing warnings (not errors) for most rules during the transition period. Key categories:
+
+| Category          | What It Catches                                                                  |
+| ----------------- | -------------------------------------------------------------------------------- |
+| **TypeScript**    | `no-explicit-any`, `no-floating-promises`, `no-unsafe-*` family, unused vars     |
+| **React**         | Display names, hooks rules (including new React Compiler rules), refresh exports |
+| **Accessibility** | Alt text, keyboard events, ARIA roles, focus management                          |
+| **Imports**       | Type imports style (`prefer-top-level`), unresolved imports                      |
+| **Promises**      | Always return, catch-or-return                                                   |
+
+## Adding New Packages
+
+When creating a new package, **you don't need to add an ESLint config**. Just ensure:
+
+1. The package has a `tsconfig.json`
+2. The `tsconfig.json` is discoverable via the pattern `{apps,packages}/*/tsconfig.json`
+
+The root config will automatically pick it up.
+
+## Suppressing Warnings
+
+If you need to suppress a specific warning:
+
+```typescript
+// Single line
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+const data: any = response;
+
+// Block
+/* eslint-disable @typescript-eslint/no-unsafe-assignment */
+// ... code
+/* eslint-enable @typescript-eslint/no-unsafe-assignment */
+```
+
+**Please use sparingly** - most warnings indicate real issues that should be fixed.
+
+## Pre-commit Hook
+
+Lint-staged runs automatically on commit via Husky:
+
+- Prettier formats your staged files
+- ESLint fixes what it can (with `--max-warnings=0`)
+
+If the commit fails due to lint errors, fix them before committing.
+
+## Reference Files
+
+- [eslint.config.mjs](../eslint.config.mjs) - Full ESLint configuration
+- [package.json](../package.json) - Available scripts
+
+## Help Us Improve!
+
+If you have the time, please consider trying to put up PRs to turn the rules I've set to `warn` to `error`, or getting all of strict mode in TypeScript working for a package (e.g., `noUncheckedIndexAccess`, `strictNullChecks`). It'll help prevent bugs at Plane, and your co-workers will unknowingly thank you for it.
+
+If you do decide to tackle this, please feel free to reach out to [@lifeiscontent](https://github.com/lifeiscontent) for advice on issues you get stuck on.
+
+Thanks!