Add Bluesky Login for DasBlog Authors (DID‑Based Auth)

[poppastring]

Allow authors to authenticate into the DasBlog admin UI using their Bluesky identity (DID). This removes the need for local passwords and aligns DasBlog with decentralized identity standards.

Proposed Solution

• Add a "Login with Bluesky" option.
• Use ATProto session creation (com.atproto.server.createSession).
• Store the DID as the author identity.
• Map DID → handle for display.
• Support session refresh tokens.

Technical Notes

• ATProto sessions are lightweight and easy to validate.
• No OAuth flow required at this stage.
• Future-proof for upcoming Bluesky authentication standards.

Acceptance Criteria

• Authors can log in using Bluesky credentials.
• Admin UI recognizes the DID as the author identity.
• Sessions persist and refresh correctly.
• No local password required.