Add Rust repository quality gates

[sidmohan0]

Objective

Establish reproducible Rust tooling and enforce basic repository hygiene before further detector growth or refactoring.

Changes

• Pin Rust 1.85.0 with rustfmt and Clippy components.
• Add a minimal Rustfmt configuration for edition 2024.
• Add CI gates for formatting, Clippy with warnings denied, and workspace tests.
• Add concise repository rules for correctness, module boundaries, binding ownership, dependencies, and scoped changes.
• Add a pull request template with the same verification contract.

No detector behavior, dependencies, or source structure are changed in this PR.

Verification

The new GitHub Actions workflow will run:

• cargo fmt --all --check
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test --workspace --all-features

If an existing workspace issue causes one of these gates to fail, that failure is useful evidence for the next scoped change rather than something hidden in this PR.