feat: v1.6.1 release

[cody-rester]

Description

Patch release 1.6.1 adding two new user-facing features, an updated What's New system, and a new What's New page for the 1.6 series.

Type of Change

• New feature

Changes Made

• --version now outputs Python version, executable path, and OS/platform info alongside the Atlas version string
• session prune --older-than DAYS bulk-deletes sessions that were created but never captured; supports --dry-run to preview and --force to skip confirmation
• What's New tracking updated to key on the minor version series (1.6) rather than exact patch version — any 1.6.x release shares the same page and is only shown once per user
• New whats-new-1.6.html page covering MongoDB log analysis, Kubernetes environment support, session prune, and --version enhancements
• Version bumped to 1.6.1 in _version.py and pyproject.toml
• CHANGELOG updated with 1.6.1 entries

Testing

• Ran platform-atlas --version — confirmed Python version, path, and OS display correctly
• Ran platform-atlas session prune --older-than 90 --dry-run — confirmed table output and no-op behavior
• Ran platform-atlas session prune --help — confirmed argument structure
• Confirmed What's New panel shows on first launch after version bump
• Verified series extraction logic: 1.6, 1.6.1, and 1.6.2 all resolve to series 1.6

Checklist

• Code follows the project's style guidelines
• Self-review of code has been performed
• Code has been commented where necessary
• Commits follow conventional format (type: subject)
• No secrets or credentials committed
• Documentation has been updated accordingly
• PR has been labeled appropriately (enhancement, bug, documentation, refactor, chore)