Generics & variance, algebraic-effect handlers, and documentation comments

[MelbourneDeveloper]

Summary

Large feature branch landing three language subsystems plus tooling/CI hardening. All CI checks were run locally and pass (see below).

• Generics & variance — crates/osprey-types/src/variance.rs, crates/osprey-ast/src/generics.rs, crates/osprey-codegen/src/effect_generics.rs; spec docs/specs/plan 0015-generics-and-variance.md. New must-reject cases in examples/failscompilation/variance_* and generic_effect_*.
• Algebraic effects & handlers — crates/osprey-ast/src/resume.rs and handler/resume codegen; plan 0016-algebraic-effects-and-handlers.md. Reject cases multishot_resume_rejected, resume_in_arm_lambda.
• Documentation comments — flavor-neutral doc model crates/osprey-ast/src/doc.rs + parser crates/osprey-syntax/src/docparse.rs; spec 0026-DocumentationComments.md, plan 0018-documentation-comments.md.
• New tested examples — fiber/fiber_determinism, fiber/fiber_exact_replica, basics/json/json_document_query (.osp/.ospml twins), registered in the example manifest.
• Duplication gate — extracted a shared osprey_ast::walk_each collection-walker (backing the freevars/effects/analysis visitors), a store_tag helper in aggregate.rs, nested/map_of_kind lowering helpers; .deslop.toml gate held at 6.10% with genuine dedup (measured 6.06%).

Test plan (run locally, in CI order)

• cargo fmt --all --check, cargo clippy --workspace --all-targets -- -D warnings — clean
• cargo build --release --workspace, cargo test --workspace — 0 failures
• Differential golden harness — PASS=142 FAIL=0 NOEXP=0, FC_OK
• npm run test:shipwright — manifest valid
• make lint — deslop 6.10% (ok); make test — all crates over coverage thresholds, extension 95.13%; make build
• Example smoke (comprehensive_math, feature_omnibus) — pass
• WASM: _runtime_wasm + compile/validate/smoke + diff_wasm_examples.sh — PASS=47 FAIL=0 SKIP=26
• Website Playwright E2E — 76 passed
• Web-compiler test.sh — pass (run against a locally-started server; the Docker daemon was unavailable on the prep host, so the container-packaging layer will be exercised by CI)

Note: ci-windows.yml is Windows-only and was not runnable on the macOS prep host; the workspace build/clippy/test it depends on all pass here.