fix(rust): use maintained Orchard grammar for pinned source

[ssmith-synaptixs]

Summary

The comment on tree-sitter-rust PR #319 identified the maintained Grammar Orchard fork, which already parses the Rust field attributes that block Spine's pinned Synaptreesitter census. Replace the optional [rust] grammar with published tree-sitter-rust-orchard==0.16.8 and adapt #[path] module handling to Orchard's nested attribute CST.

This also updates Rust validation records and checks source-only grammar installation on macOS and Windows in CI. Upstream PR #319 can remain open; this change does not depend on its merge.

Validation

• Pinned Synaptreesitter 867aa6d: 109/109 tracked .rs files parse without ERROR (stock grammar: one file, four error lines). Pinned itoa: 5/5 clean.
• Rust-only Synaptreesitter graph: 4,703 nodes, 8,186 edges; verify_batch has zero errors and warnings, matching the previous patched-grammar baseline.
• orchestrator pkg accuracy --check: zero gated regressions. Focused extractor/scope/verifier/grounding/doctor tests: 151 passed; dedicated syntax regression passes.
• Locked install with CI language extras built Orchard locally. Ruff, mypy, strict docs audit, roadmap status, architecture, and lock checks passed.
• Full local suite before the new test count was recorded: 5,485 passed, 13 skipped, one failed on the count. After updating that count, the affected tests passed (13/13). Full PR CI passed, including the main suite and the macOS/Windows grammar-install jobs.

Remaining gates

• Orchard 0.16.8 is a source-only PyPI release and needs a C compiler. The initial macOS build hit this machine's malformed Command Line Tools SDK; Homebrew LLVM with Xcode 26.2 built it. The new macOS/Windows CI jobs passed with the default runner install path.
• Synaptreesitter's existing strict Clippy baseline remains red, so this PR does not claim Core Rust release readiness.

Details: docs/evals/rust-orchard-grammar-validation.md.