feat(exec): show container config in executable detail views

[jahvon]

Summary

Follow-up to the containerized-executions feature (#407): neither executable detail view surfaced the container: config.

• flow get (markdown) — shellExecMarkdown rendered dir/logMode/cmd/file but not container.
• flow browse (TUI detail) — shellExecConfig had the same gap.

Adds a shared executable.ContainerConfigMarkdown renderer and wires it into both paths, so image, runtime, workspace mount, volumes, user, network, and entrypoint are shown. Effective values are displayed, so SetDefaults-applied fields (runtime auto, mount /workspace) are visible.

Example rendered block:

**Container**
- Image: `golang:1.21-alpine`
- Runtime: auto
- Workspace mount: `/workspace`
- Volume: `//cache:/cache`
- User: `1000:1000`
- Network: `host`
- Entrypoint: image default

Testing

• Unit test for ContainerConfigMarkdown (nil → empty; all fields present; entrypoint: "" → "image default").
• Verified the full Executable.Markdown() path includes the block.
• Full unit suite + lint clean.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 76.92308% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
types/executable/container.go	76.92%	3 Missing and 3 partials ⚠️

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