feat(compiler): implement Stage 36 property hooks

[amasiye]

Summary

Implement Stage 36 property hooks under Decision 0135 through the checked compiler pipeline.

• Computed and automatically backed getters/setters, explicit writable get, borrowed get, typed setter inputs, and checked effects.
• Concrete, interface, constrained-generic, trait, and inherited accessor dispatch; exactly-once read-modify-write.
• Parent declaration initializers run before child initializers over one inherited backing slot. Replacement acquires the child value before releasing the parent value, without invoking setters. Failed construction cleans initialized fields and completed ancestor phases only.
• Shared ownership/provenance fixes distinguish an owned return carrier from the source it retains, preserve repeatable captures, and keep nullable and selected-place borrows sound across the backends.
• Transitive nonblocking analysis includes helpers, callbacks, and cleanup. PHP nominal names are isolated from host reserved names and case folding.

Removed Or Corrected Boundaries

• Remove the blanket E0764 hook-execution rejection.
• Remove false readonly-collection-read and shared-handle-return-borrow rejections, premature repeatable-capture cleanup, and spurious ambient I/O effects only where actual callback provenance proves otherwise.
• Reject genuinely blocking/async hook work transitively, including output.
• Preserve PHP's existing numeric compatibility diagnostics; do not substitute host overflow or float-formatting semantics.

Validation

• php scripts/validate_work_unit.php --llvm: passed on macOS ARM64, including formatting, both Clippy configurations, production builds, workspace tests, and LLVM suites.
• Durable native manifest: all 389 examples pass interpreter/Cranelift/LLVM comparison of output, status, and declared file effects. Both default and LLVM parity suites passed all 11 tests.
• Property hooks: 87 tests; parent/child initialization: 16 tests. PHP, ownership, cleanup, malformed-MIR, and retained-closure regressions passed.
• macOS leak checks on successful and failing parent/child initialization report zero leaks with both native backends. The checker reports restricted-process memory visibility; a prior positive control confirmed leak detection. Linux Valgrind coverage is wired into CI and is not claimed as locally executed.
• Documentation authority, diagnostic style, build-artifact policy, remote dependency pins, and diff checks passed.
• Exact-head Linux/macOS/Windows CI remains the merge gate.

Invalidated Elsewhere

Language-server traversal, highlighting, hover, navigation, receiver/accessor facts, diagnostics, and compiler pin require the coordinated Stage 36 update. Website guides, API reference, tutorials, and playground examples must retain the accepted target-state contracts. Companion integration and installed-toolchain refresh are still pending; this PR does not yet claim overall Stage 36 closure.

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