dev-null.sh integration

What was done

Added a /dev/null integration to MagicSync so users can publish "commits" (posts) to dev-null.sh, a developer social network. Writes to dev-null.sh are authenticated by SSH signatures verified against keys published on the author's GitHub account, so the integration is gated on a GitHub connection.

How it works

1. GitHub provider (better-auth) — users connect GitHub (NUXT_GITHUB_CLIENT_ID / NUXT_GITHUB_CLIENT_SECRET). Scopes: read:user, user:email, admin:public_key.
2. Platform devnull — added to platformConfigurations (4000-char limit, 3 images, JPEG/PNG/WebP ≤10 MB).
3. Scheduler plugin DevNullPlugin signs the commit payload with ssh-keygen -Y sign and POSTs to https://dev-null.sh/api/cli/commits.
4. Connection UI — ConnectAddAccount.vue opens a DevNullSetup.vue modal with two tabs:
   • Guided (default, Option C) — terminal/GitHub-Actions steps; MagicSync never stores a key.
   • Stored key (opt-in, Option A) — generates a dedicated Ed25519 key, stores it encrypted, registers the public half on GitHub. Requires explicit risk acknowledgement.

Security mitigations (Option A)

• Dedicated single-purpose key; never the user's real SSH key.
• Private key encrypted at rest via better-auth/crypto (BETTER_AUTH_SECRET).
• Explicit opt-in with risk disclosure; default stays guided (no storage).
• Revocation removes the key from both MagicSync and GitHub.
• Audit logging for generate/register/revoke/post.
• Rate-limit aware (10 submissions/min/user).

Prerequisites

• User must connect GitHub first.
• User must sign in to dev-null.sh at least once (so a /dev/null account exists).

Limitations (dev-null.sh public API)

dev-null.sh's terminal/SSH interface only supports: body, --reply, and up to 3 images. The following dev-null.sh features are not reachable from MagicSync today:

• Polls and voting — composer-only on dev-null.sh.
• Quoting a commit — separate action, not exposed via the terminal interface.
• Remotes (direct messages) / Orgs — no public write or read API for DMs.
• Comments listing — the public read API exposes replies_count but no replies endpoint; MagicSync shows the count as an insight instead.

Stats (stars, replies) and image/link-preview metadata are fetched via GET /api/v1/commits/{id} and surfaced as post insights.

Files touched

• packages/auth/lib/auth.ts — github social provider + trustedProviders
• packages/shared/shared/platformConstants.ts — devnull platform config
• packages/db/.../social-media-account.service.ts — devnull in platform union
• packages/db/.../plugins/devnull.plugin.ts — new plugin
• packages/db/package.json — better-auth dependency
• packages/scheduler/.../AutoPost.service.ts — register plugin
• packages/connect/.../useConnectionManager.ts — github + devnull connections
• packages/connect/.../ConnectAddAccount.vue — wire modal
• packages/connect/.../DevNullSetup.vue + .json — setup UI + copy
• packages/connect/server/api/v1/social-accounts/devnull/setup.post.ts
• packages/connect/server/api/v1/social-accounts/devnull/revoke.post.ts