feat(bindings): apply pdf annotations from every binding

[andiwand]

🤖 Generated with Claude Code

Phase 6, the last of docs/design/pdf-annotation.md. Stacked on #849.

binding	surface
python	PdfFile.annotate(annotations) -> bytes
java	PdfFile.annotate(String) -> byte[]
swift / ObjC	PdfFile.annotate(_:) throws -> Data
wasm	handle.annotate(annotations) -> Uint8Array

Plus the annotate capability on FileTypeCapabilities in all four.

Each returns the annotated bytes rather than writing a file — none of these callers has a filesystem the caller would want written to, and the wasm one least of all. That matches how save() already works in wasm and python.

Fixtures

Each binding needed a pdf to test against, and each builds one the way its neighbours build theirs — inline, with the cross-reference offsets computed rather than hardcoded, so no test data is fetched. Four small generators: python conftest.py, java TestFiles, swift Fixture, wasm helper.mjs.

Each suite then checks the same three things: the source comes back as a prefix of the result (the incremental update is visible from the outside), the annotation is in what follows, and a payload this build does not understand is refused with that binding's error type.

All four built and run

• python — 75 tests pass (4 new)
• JNI — 56 tests pass, up from 53. The new test class had to be listed in jni/CMakeLists.txt; without that it compiles into nothing and the suite silently stays at 53, which is what happened on the first run here.
• wasm — 42 node tests pass (3 new), built through the emscripten toolchain
• Apple — both macOS slices built, xcframework assembled, 34 XCTest cases pass (3 new)

Changelog entry extended to name the bindings and odr.annotation.

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That completes the plan in docs/design/pdf-annotation.md, whose status is now landed.