fix(extract): skip declare ambient class properties in class-member extraction

[BartWaardenburg]

DRAFT: Reviewer verdict was FIX. The following must be resolved before merge:

• Bump CACHE_VERSION from 106 to 107 in crates/extract/src/cache/types.rs (line 108) and add a doc paragraph explaining that pre-fix caches may retain the declare member as unused until the file is re-extracted.

Summary

Added a && !prop.declare guard in the ClassElement::PropertyDefinition arm of extract_class_members in crates/extract/src/visitor/helpers.rs. TypeScript declare properties are ambient-only (no emitted JS) and cannot be value-referenced, so they must not appear as extracted class members. The regression test declare_ambient_property_excluded_from_class_members parses a class with a declare readonly __input?: I field plus a normal method and asserts the ambient field is absent from extracted members while the method is present.

Review

Verdict: FIX

• Missing CACHE_VERSION bump. extract_class_members output is persisted in the parse cache (CachedExport.members: Vec<CachedMember> in crates/extract/src/cache/types.rs:326, CACHE_VERSION=106). The fix changes the content of cached member data (now omits the declare member), an extraction-semantics change. Without bumping 106 to 107, a user upgrading to get this fix keeps the stale cached __input member and the false unused-class-member finding persists across the upgrade until each affected file is touched. The assertion at cache/types.rs:145 explicitly triggers on "wire shape OR extraction semantics."
• Non-blocking: the core guard, test, clippy, and fmt are all clean and correct. Only the cache-version omission blocks merge.

Closes #839