fix: migrate Java examples to Spring Shell 4

[arnabnandy7]

Summary

• Align the Java examples with Spring Shell 4.0.2.
• Remove the explicit Spring Shell 3.4 dependency that produced a mixed 3.4/4.0 runtime.
• Migrate example shell commands from @ShellComponent, @ShellMethod, and @ShellOption to Spring Shell 4 annotations.
• Preserve existing command names such as string-joke, object-joke, travel-report, bank-support, and cook.

Background

This is a downstream compatibility update for:

• Upgrade to Spring Shell 4.x embabel-agent#1720
• fix: upgrade to Spring Shell 4 embabel-agent#1956

Before this change, the examples selected Spring Shell 3.4 core and starter artifacts alongside Spring Shell 4.0.2 components supplied by Embabel Agent. The resulting mixed classpath prevented migrated Embabel commands from being registered correctly.

Verification

• Confirmed the dependency tree resolves Spring Shell artifacts consistently at version 4.0.2.
• Compiled examples-java against embabel-agent.version=1.5.2-SNAPSHOT.
• Confirmed git diff --check passes.
• Run the Java horoscope example interactively and verify help, command discovery, and tab completion.
• Run the complete repository test suite.

Closes #137.