feat: support --sdk switch with built-in base roles (#378)

[bradygaster]

Summary

When squad init --roles --sdk is used, generates TypeScript config files using useRole() from the SDK's role catalog instead of plain defineAgent() calls.

What changed

SDK (packages/squad-sdk/src/config/init.ts):

• Added roles?: boolean to InitOptions
• New generateSDKBuilderConfigWithRoles() function emits useRole() calls for base role agents and defineAgent() for system agents (scribe, ralph)
• Default starter team (lead, backend, frontend, tester) generated when no explicit base-role agents provided

CLI (packages/squad-cli/src/cli/core/init.ts):

• Passes --roles flag through to SDK InitOptions

Tests (test/init-sdk.test.ts):

• 8 new tests covering: sdk+roles generates useRole, non-role agents keep defineAgent, role catalog comment, valid export, explicit role agents, sdk-only unchanged, roles-only unchanged

How it works

squad init --sdk --roles generates a squad.config.ts like:

\\ ypescript
import {
defineSquad,
defineTeam,
defineAgent,
useRole,
} from '@bradygaster/squad-sdk';

const lead = useRole('lead', { name: 'lead' });
const backend = useRole('backend', { name: 'backend' });
const frontend = useRole('frontend', { name: 'frontend' });
const tester = useRole('tester', { name: 'tester' });

const scribe = defineAgent({ name: 'scribe', ... });
const ralph = defineAgent({ name: 'ralph', ... });

export default defineSquad({ ... });
\\

Test results

• Build: clean (0 errors)
• Tests: 4,206 passed, 5 skipped, 46 todo (baseline was 4,199 + 8 new = 4,207, minus 1 pre-existing aspire Docker failure)

Working as EECOM (Core Dev).

Closes #378