feat!: SocialPlatformsResponse becomes ordered { platforms: SocialPlatformConfig[] }

[chubes4]

Summary

Mirrors the breaking REST contract change in data-machine-socials#131. The /platforms endpoint now returns an ordered array under a { platforms: [...] } envelope with slug and canonical capabilities always present on every entry. This PR updates the typed wrapper to match.

Changes

Before

export interface SocialPlatformConfig {
  label: string;
  authenticated: boolean;
  username: string | null;
  // ... no slug, no capabilities
}

export type SocialPlatformsResponse = Record<string, SocialPlatformConfig>;

After

export interface SocialPlatformCapability {
  slug: string;
  label: string;
}

export interface SocialPlatformConfig {
  slug: string;                              // ← now required
  label: string;
  type: string;                              // ← now required
  authenticated: boolean;
  username: string | null;
  capabilities: SocialPlatformCapability[];  // ← now required, canonical shape
  // ... rest of fields unchanged
}

export interface SocialPlatformsResponse {
  platforms: SocialPlatformConfig[];         // ← array, ordered
}

SocialsResource.getPlatforms() signature is unchanged on disk (Promise<SocialPlatformsResponse>); only the underlying type shape changed.

Why

• platforms array — server controls display order (authenticated-first then A-Z), clients render in iteration order. No more relying on JS object key insertion order.
• slug always present — clients no longer reconstruct it from object keys.
• Canonical capabilities shape — kills the string[] legacy fallback in client code (server-side normalize_capabilities handles legacy handler output before serialization).

Coordinated rollout

This is PR B of a 3-PR cluster:

1. data-machine-socials#131 — REST contract
2. B (this PR) — typed wrapper
3. extrachill-studio (next) — consumer

Studio + any other api-client consumer will break against the new server response until C lands. Order: A → B → C, deploy in same order.

Test plan

• ✅ npx tsc --noEmit clean
• ✅ npm run build clean (CJS + ESM + DTS bundles)
• ⏳ Studio sidebar regression check after PR C deploys