fix(social): harden Mastodon status publishing

[davethediver1010-cmd]

Summary

• Rebased the Mastodon branch on current master after feat: publish Mastodon social posts #62 landed.
• Narrowed this from a duplicate adapter implementation into incremental hardening for the existing Mastodon adapter.
• Preserves link + hashtag formatting, normalizes instance URLs for token lookup/account IDs, surfaces Mastodon API error messages, and rejects media attachments until uploads are implemented.

Verification

• pnpm test -- packages/social/mastodon/src/index.test.ts
• pnpm --filter @profullstack/sh1pt-social-mastodon typecheck

Note

• Repo-wide pnpm typecheck still fails in packages/agent-providers/shared before this package due to existing tsconfig/module-resolution errors unrelated to this PR.

[davethediver1010-cmd]

Local verification passes:

• pnpm test -- packages/social/mastodon/src/index.test.ts
• pnpm --filter @profullstack/sh1pt-social-mastodon typecheck
• pnpm --filter @profullstack/sh1pt-social-mastodon build

The failing GitHub check appears to be repository CodeQL configuration, not this patch. The job log reports: "CodeQL analyses from advanced configurations cannot be processed when the default setup is enabled."