version: bump to 3.1.1

[damachine]

Change:

Separates access_token into a standalone credentials.json file that
is auto-created and managed by the daemon.

Credentials

• credentials.json auto-created on first startup with empty token
• Token auto-persisted from config.json → credentials.json on load
• config.json auto-normalized from compact to pretty-printed format
• access_token removed from shipped config.json template

Code Cleanup

• Removed unused multipart CURL helpers
• Unified CURL reset
• Eliminate duplication

Packaging

• Debian: added conffiles for config protection
• All formats: updated for credentials.json handling