Feature 06: Symlink and Extension Handling for SPEC UI/API

DAG store behavior was improved for symlinked roots/files and extension resolution.

Delivered Improvements

• Symlink-aware DAG root resolution in DAG store.

• Recursive DAG discovery uses resolved roots consistently.

• SPEC lookup preserves real extension handling for both .yaml and .yml.

• Dedicated regression tests for symlinked roots/files and .yml access.

Files

• internal/persistence/local/dag_store.go

• internal/persistence/local/dag_store_test.go