Add Rust-owned Java baseline extraction

[jununfly]

Roadmap

• Roadmap id: rust-owned-java-support
• Roadmap branch: codex/rust-owned-java-support
• Closeout status: complete
• Closeout commit: 7dd05003
• Post-merge branch cleanup plan: delete codex/rust-owned-java-support

Scope

• Implements the Java item from docs/prds/2026-07-03-rust-owned-migration-roadmap.md.
• Moves Java baseline extraction to Rust-owned indexing.
• Removes the TypeScript Java fallback extractor implementation.
• Keeps Spring/Play/framework semantics in the TypeScript shell.

Verification

• cargo build --package zcodegraph-core
• npm run build
• npx vitest run __tests__/rust-index-engine-cli-language-smoke.test.ts
• npx vitest run __tests__/frameworks-integration.test.ts __tests__/resolution.test.ts
• GitHub corpus validation: spring-projects/spring-petclinic at b3ee2c5

Evidence

• Java is listed as Rust-owned in rust-hybrid metadata.
• Java-only smoke shows fallbackFileCount: 0.
• Petclinic validation indexed 72 files with engineByLanguage.java = rust; remaining fallback files are non-Java resources only.
• Corpus evidence recorded in docs/benchmarks/2026-07-03-rust-owned-java-spring-petclinic-validation.md.

Closeout

• PRD checklist updated.
• Process roadmap files deleted.
• Durable decisions retained in the PRD and benchmark evidence doc.