refactor(cli): extract arg parsers

[kunaldhongade]

Refs #262

Summary

• Moves CLI command argument parsing into packages/cli/src/parsers/args.ts.
• Keeps packages/cli/src/index.ts focused on command wiring and execution.
• Preserves the existing parser behavior and public CLI surface.

Validation

• pnpm install
• pnpm run lint
• pnpm typecheck
• pnpm exec vitest run packages/cli/test/cli.test.ts packages/cli/test/built-cli.test.ts packages/core/test/core.test.ts
• pnpm test
• pnpm build
• pnpm --filter @submuxhq/codedecay pack --dry-run
• node packages/cli/dist/index.js --help
• node packages/cli/dist/index.js analyze --format markdown
• node packages/cli/dist/index.js analyze --format yaml exits 2
• node packages/cli/dist/index.js analze exits 2 with suggestion
• node packages/cli/dist/index.js version