chore: raise MSRV to Rust 1.99

[shunichironomura]

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Summary

• Raise the workspace MSRV from Rust 1.95 to 1.99, matching the existing pinned development toolchain.
• Update the English and Japanese installation requirements.
• Isolate the nested report-engine build from inherited dynamic-library search paths so identical Rust installations cannot select the host compiler's sysroot; add regression coverage while preserving PATH for tool discovery.
• Update the pinned Miri/AddressSanitizer nightly to a Rust 1.99-compatible version.
• Prebuilt binary users are unaffected; source builders, Rust library consumers, and plugin authors need Rust 1.99 or later. No Graphcal source syntax or semantics change.

Validation

• just lint
• just test
• cargo +1.99.0 check --workspace --all-targets --locked
• just docs-build
• cargo hack check --workspace --rust-version --ignore-private with Wasm absent from the MSRV 1.99 installation and present only in the pinned 1.99.0 installation
• cargo test --locked -p graphcal --test report_engine (7 tests passed)
• Plugin ABI memory tests under Miri on nightly-2026-07-10 with symbolic alignment checks and Tree Borrows (5 tests passed)
• zizmor --offline .github/workflows/ci.yaml .github/workflows/dynamic-safety.yaml

AI assistance

• AI used: yes — investigated the MSRV options, edited the workspace manifest and installation requirements, ran validation, and prepared this PR.
• Human review of AI-assisted code: pending

Breaking changes

• No breaking changes
• Breaking changes; the breaking change label is applied