[QuantumExplorer]

Fixes #107.

Problem

Mode::default() is NoCors. fetch's default mode is cors, and a grpc-web call does not work in no-cors mode across origins, because its headers are not CORS-safelisted and the response is opaque. FetchOptions::new().mode(Mode::default()) makes every call fail with JS API error: TypeError: Failed to fetch. Mode::Navigate can never work either, since fetch rejects every request whose mode is navigate. #107 has a reproduction for both.

Fix

• Cors is the #[default] variant, matching fetch. The NoCors docs say why a grpc-web call cannot work in that mode.
• Navigate is deprecated rather than removed, so code that names it keeps compiling.

FetchOptions::default() leaves the mode unset, so only code that asks for Mode::default() sees a change.

Before and after

Code	Before	After
FetchOptions::new().mode(Mode::default())	no-cors, every call fails with Failed to fetch	cors, calls work
FetchOptions::new()	mode unset, the browser's default (cors)	unchanged
FetchOptions::new().mode(Mode::Navigate)	every call fails	every call fails, and the compiler warns that Navigate is deprecated

Tests

Unit test default_is_cors_like_fetch in src/options/mode.rs.

cargo fmt --check, cargo clippy --all-targets -- -D warnings, cargo clippy --target wasm32-unknown-unknown -- -D warnings and cargo test are clean, and the browser suite in test-suite/simple passes in headless Chrome 153.

This is one of 14 PRs from the review asked for in #97. They are independent, and all 14 also merge together cleanly; with all of them merged, both browser suites (test-suite/simple and test-suite/gzip) pass.

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