Align Java formatting with shared just recipes

[roji]

Java is the only SDK with a repository-managed pre-commit formatting hook; the other SDKs use explicit local commands backed by CI. The hook also checks working-tree contents rather than the staged snapshot, so it is not reliable enforcement of what gets committed.

Replace the hook and its automatic installation with just format-java (Spotless) and just lint-java (Spotless and Checkstyle), and include Java in the aggregate just format and just lint recipes. Update the development documentation with these commands and their Maven equivalents.

Existing Spotless and Checkstyle CI enforcement remains unchanged. Spotless continues to run explicitly in CI because mvn verify alone does not check formatting.

[Copilot]

Copilot review overview

🟢 Approval recommended

The commands match the Maven configuration and existing CI enforcement.

Review tier: Balanced
Findings: None

What changed in this PR

Aligns Java formatting and linting with shared repository just workflows while removing the unreliable pre-commit hook.

Changes:

• Adds Java to aggregate formatting and linting recipes.
• Documents just and equivalent Maven commands.
• Removes pre-commit hook installation and implementation.

File	Description
justfile	Adds Java format and lint recipes.
java/​README.md	Documents Java formatting and linting.
.github/​workflows/​copilot-setup-steps.yml	Stops installing the pre-commit hook.
.github/​copilot-instructions.md	Updates Java development guidance.
.githooks/​pre-commit	Removes the Java formatting hook.

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[edburns]

I approve this and will also state so in the PR.