fix: Fix visual continuity in docker isolation mode

[konard]

Summary

Fixes #73

The empty line in docker isolation output is now correctly placed AFTER the command line ($ docker pull alpine:latest) instead of BEFORE it, maintaining consistent visual structure in the timeline output.

Problem

When running $ --isolated docker -- echo 'hi', there was an empty line between the timeline marker (│) and the virtual command ($ docker pull):

│

$ docker pull alpine:latest
latest: Pulling from library/alpine

Solution

Move the empty line from before the command to after it:

│
$ docker pull alpine:latest

latest: Pulling from library/alpine

Changes

JavaScript:

• cli.js: Skip empty line after start block when deferCommand is true
• docker-utils.js: Add empty line after virtual command print, remove it before result marker

Rust:

• main.rs: Skip println!() after start block when is_docker_isolation is true
• isolation.rs: Add empty line after virtual command print, remove it before result marker

Tests:

• Added visual continuity tests in both JS (output-blocks.test.js) and Rust (output_blocks_test.rs)

Test plan

• Unit tests pass in JavaScript (bun test)
• Unit tests pass in Rust (cargo test)
• Linting passes (eslint, cargo clippy)
• Formatting passes (prettier, cargo fmt)
• CI passes

🤖 Generated with Claude Code

[konard]

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