feat: container support (#171)

* docs: fix container Quick Start to use writable output volumes

Users were unable to access reports because examples used ephemeral
container /tmp directory. Updated all examples to show proper pattern:
- Mount writable host directory for output
- Use mounted path for --output-dir
- Reports now accessible on host filesystem

Changes:
- CONTAINER.md: Updated Quick Start, Usage, CI/CD examples
- README.md: Updated Container (Recommended) section
- Added troubleshooting section for ephemeral filesystem issue
- Removed confusing "Save Output Files" section (integrated into examples)

Fixes issue where `podman run --rm -v /repo:/repo:ro agentready assess /repo --output-dir /tmp`
writes reports inside container's ephemeral /tmp, destroyed on exit.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: update bundler to v2.5.23 for Dependabot compatibility

Dependabot only supports bundler v2.* but Gemfile.lock specified v1.17.2.
Updated BUNDLED WITH section to use bundler 2.5.23.

Fixes Dependabot error:
"Dependabot detected the following bundler requirement for your project: '1'.
Currently, the following bundler versions are supported in Dependabot: v2.*."

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

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Co-authored-by: Claude <noreply@anthropic.com>

Author: jeremyeder