feat: migrate to Bun-native APIs and add Zod validation

[betegon]

Summary

Migrate the CLI to use Bun-native APIs following best practices from OpenCode's implementation. This improves performance, reduces dependencies, and provides a better developer experience.

Changes

Bun API Migration

• File I/O: Replace node:fs with Bun.file() and Bun.write() for async file operations
• Process spawning: Replace child_process with Bun.spawn() and Bun.which()
• File discovery: Replace manual directory traversal with Bun.Glob
• Sleep: Use Bun.sleep() instead of setTimeout wrapper

Validation

• Add Zod for runtime config validation with schemas
• Types are now inferred from Zod schemas

Build System

• Replace fossilize with native Bun.build({ compile: true })
• Support for 5 standard targets + 3 baseline (no AVX2) targets
• New build commands:
  • bun run build - Current platform
  • bun run build:all - All platforms
  • bun run build:baseline - Include baseline builds

Developer Experience

• Add .cursor/rules/bun-cli.mdc with comprehensive Bun development standards
• Links to Bun docs for each API

Breaking Changes

All config functions are now async:

// Before
const token = getAuthToken();
const isAuth = isAuthenticated();

// After  
const token = await getAuthToken();
const isAuth = await isAuthenticated();

Testing

• CLI runs: bun run dev --help
• Build works: bun run build creates working binary
• Binary runs: ./dist/sentry-darwin-arm64 --help

Files Changed

Category	Files
Rule file	.cursor/rules/bun-cli.mdc
Build	script/build.ts, package.json
Types	types/config.ts, types/dsn.ts, types/index.ts
Lib	config.ts, browser.ts, dsn-detector.ts, api-client.ts, oauth.ts
Commands	auth/*.ts, issue/*.ts, project/list.ts