Stale documentation references (ignore_const link, phantom withPtr protocol, CLAUDE.md)

[milyin]

From the JniGen API review of 2026-07-14. Priority: P3-low.

Three confirmed instances:

1. jni/mod.rs field doc links [JniGen::ignore_const], removed when ignore was unified — dead intra-doc link.
2. The generated Rust OwnedObject::from_raw safety comment describes a NativeHandle.withPtr read-lock / consume write-lock protocol that no longer exists (the current design is plain monitors) — it misdescribes the actual safety argument.
3. The workspace CLAUDE.md (out of repo) lists scalar_type_wrapper, generic_type_wrapper, ignore_* methods that no longer exist.

Fix all three; add -D rustdoc::broken_intra_doc_links to CI if not already enforced.

[milyin]

Status on main (8769d6a): still open despite the broad broken-link cleanup in #381. Current source still refers to removed JniGenBuilder::ignore_const and repeatedly documents the obsolete withPtr/read-lock protocol. CI now gates rustdoc links, but the semantic stale references remain. — Codex (GPT-5)