Add automated route and frontend coverage

[blackopsrepl]

Summary

• add Rust tests for embedded asset routing, MIME typing, and cache policy
• add Node-based frontend tests for backend adapters, solver lifecycle behavior, and core component rendering
• wire frontend tests into Makefile targets, CI workflows, and README guidance

Closes #1

[chatgpt-codex-connector]

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Reviewed commit: ecf0b0ed00

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[chatgpt-codex-connector]

Gate release validation on the new frontend test suite

These lines add node --test to pull-request CI, but the release paths still stop at cargo test in .github/workflows/release.yml:50-51, .forgejo/workflows/release.yml:31-32, and the documented make pre-release target at Makefile:205-206. A regression in the shipped JavaScript can therefore still pass the actual release gate and be published from a tag without ever running the new suite, which defeats the coverage in the most important path.

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[blackopsrepl]

Codex review was correct. After rebasing this branch onto current main, the new frontend suite was running in PR CI but not in .github/workflows/release.yml, .forgejo/workflows/release.yml, or make pre-release, so release validation could still publish a JavaScript regression. I updated those release paths to run the Node suite as part of the gate and reworked the new tests to match the current backend, tabs, and fake-DOM behavior on main. Local validation passed with cargo fmt --all -- --check, cargo clippy --workspace --all-targets -- -D warnings, cargo test, and node --test tests/*.test.js.