Monoscope v0.6.31

CLI fixes and workflow improvements:

• Center historical events context --at windows correctly.
• Mask credential entry and output; write credential files with private permissions.
• Show help consistently for every command and improve errors in scripts.
• Reject invalid durations, nonpositive search limits, and unknown chart types.
• Correct the custom installation-directory example.
• Report the release version correctly and recognize already installed releases without redundant downloads or failure exits.

Breaking change: metrics query --assert exits with failure when the query has no numeric scalar. Use summarize without a by clause for assertion queries.

Credential files use 0600, and the config directory uses 0700, including existing files and directories.

Validation includes 127 CLI workflow tests, real PostgreSQL and TimeFusion context checks, 176 browser tests, credential-entry checks, and binary linkage checks.