fix(extract): emit inherits edge for JavaScript class extends

[Synvoya]

Bug

Plain JavaScript class heritage was dropped: class Dog extends Animal {} emitted no inherits edge, while the equivalent TypeScript did.

Root cause

The JavaScript grammar stores extends and its identifier directly under class_heritage. TypeScript wraps the base in an extends_clause. The walker only handled the wrapped shape.

Fix

When a class_heritage node has no extends_clause or implements_clause, treat the heritage node itself as the JavaScript extends clause. The guard preserves the existing TypeScript path and prevents duplicate edges.

The implementation remains precision-first: direct same-file and imported identifiers resolve; runtime expressions such as extends mixin(Animal) are not converted into fabricated static inheritance. Qualified member expressions require namespace-aware resolution and remain outside this focused fix.

Validation

• Added same-file JavaScript inheritance coverage.
• Added imported JavaScript inheritance coverage.
• Added a dynamic-base negative control.
• Existing TypeScript interface, generic, imported and implements cases remain covered.
• tests/test_ts_inheritance.py: 10 passed.
• Ruff and git diff --check: passed.

[Synvoya]

Follow-up audit against current v8 found that JavaScript member-expression parents such as class Dog extends ns.Animal were still dropped. The branch now handles that AST shape and adds a regression test. Current validation: tests/test_ts_inheritance.py 9 passed; Ruff and git diff --check passed.

[Synvoya]

Precision follow-up: I removed the member-expression tail normalization mentioned in my previous comment. Treating ns.Animal as bare Animal can falsely bind an unrelated same-file class without namespace-aware resolution. The final branch stays focused on direct JavaScript heritage identifiers, adds imported-class coverage and a runtime-expression negative control, and is squashed to one commit.