feat: Facebook Page integration
Four tools: facebook_get_page, facebook_get_posts, facebook_create_post
(text + optional link), facebook_create_photo_post (image URL + caption).
Uses Graph API v19.0 with Page access token. Credentials stored per-customer
in Redis under creds:{id}:facebook with pageId alongside the access token.
Env-var fallback: FACEBOOK_{ACCOUNT}_ACCESS_TOKEN + FACEBOOK_{ACCOUNT}_PAGE_ID.
Wired into Platform type, validPlatforms, /api/connections, manifest OpenAPI
spec, and manifest tool registry.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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