chore: AI code quality improvements (run 28770102825)

[github-actions]

Summary

Automated PR from the AI Code Quality Agent (run 28770102825).

Changes may include (per CONVENTIONS.MD)

• Auto-formatting via Spotless (Java) and Prettier (JS/TS)
• Javadoc added to public classes / interfaces that had none
• Immutability first: List.of() / Set.of() replaced with Guava ImmutableList.of() / ImmutableSet.of(); Collectors.toSet() replaced with ImmutableSet.toImmutableSet()
• Ordered mutability: HashMap → LinkedHashMap, HashSet → LinkedHashSet; Collectors.toMap → PepperStreamHelperHacked.toLinkedMap; Collectors.groupingBy with LinkedHashMap::new
• Logging: SLF4J {} placeholders instead of string concatenation
• Method ordering: recently-touched files reordered to follow the Stepdown Rule (entry points first, callees below their first caller)

Review checklist

• CI passes (Build, Spotless, Static Analysis)
• No unintended logic changes
• Javadoc is accurate and meaningful
• Review .github/ai-quality-discoveries.md — promote confirmed new patterns to CLAUDE.md, discard false positives