Add Gradle/Java source-level extractor support

[MichaelSNelson]

Summary

• Adds a new extractor pipeline for Gradle-based Java projects (src/codezoom/extractors/gradle/)
• Uses javalang for source-level AST parsing — no JDK or bytecode required
• Extracts module hierarchy, inter-module dependency graph, and full symbol data (classes, methods, fields, call graphs, visibility, line numbers, inheritance)
• Detects Gradle projects via build.gradle.kts / build.gradle and auto-selects extractors
• Extracts project name from settings.gradle.kts / build.gradle.kts

New files

File	Purpose
extractors/gradle/__init__.py	Re-exports the three extractor classes
extractors/gradle/gradle_deps.py	Inter-module dependency graph from source imports
extractors/gradle/source_hierarchy.py	Package/module hierarchy from source tree
extractors/gradle/source_symbols.py	Full symbol extraction via javalang AST parsing

Modified files

• pyproject.toml — adds javalang as optional [gradle] dependency
• detect.py — auto-detects Gradle projects and registers extractors
• pipeline.py — Gradle project name guessing + skip package discovery for Gradle projects

Test plan

• Tested against multiple Gradle-based QuPath extension projects
• Verified codemap JSON output includes hierarchy, imports, and symbol data
• Upstream review and feedback

🤖 Generated with Claude Code

[ctrueden]

Thanks for the PR, @MichaelSNelson! I rebased it over the current main branch, and added a commit to remove the use of javalang, because that project can't handle newer versions of Java used by QuPath. Could you give it a try on your QuPath extensions and let me know how it goes? Or even just point me at a project you'd like me to use for further testing?