fix(config): preserve React language IDs for TSX/JSX

[dergachoff]

Summary

Fixes #148.

This keeps React document language IDs intact for TSX/JSX files and still lets the common single TypeScript or JavaScript server configuration handle them.

• typescript + .tsx file patterns now map to typescriptreact
• javascript + .jsx file patterns now map to javascriptreact
• when no exact react LSP client is configured, typescriptreact routes to the typescript server and javascriptreact routes to the javascript server
• if an exact react server is configured, it wins over the fallback

The existing C/C++ file-pattern override behavior is unchanged.

Validation

• cargo +nightly fmt --check
• cargo +1.95 clippy -p mcpls-core --all-targets --all-features -- -D warnings
• cargo +1.95 test -p mcpls-core
• cargo +1.95 nextest run -p mcpls-core
• cargo +1.95 test -p mcpls-core get_client_for_file
• Built a local release binary from a combined branch containing this PR plus fix(lsp): omit null diagnostic request fields #147, then ran a standalone MCP stdio probe against a real TSX project using tsgo. get_diagnostics returned empty diagnostics for both a TSX source file and a TSX test file, with no typescriptreact no-server error and no identifier:null protocol error.

[Copilot]

Pull request overview

This PR fixes React TSX/JSX files being opened with non-React LSP language IDs when extension mappings are inferred from LSP server file_patterns, ensuring .tsx uses typescriptreact and .jsx uses javascriptreact while still allowing fallback routing to the base TypeScript/JavaScript server when no React-specific server is configured.

Changes:

• Derive typescriptreact/javascriptreact language IDs from .tsx/.jsx patterns even when the server’s language_id is typescript/javascript.
• Add fallback client routing so typescriptreact → typescript and javascriptreact → javascript when no exact React client is registered.
• Add unit tests covering the new extension-map derivation and client routing behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
crates/mcpls-core/src/config/mod.rs	Adds pattern-extension language ID derivation for TSX/JSX and tests for the effective extension map.
crates/mcpls-core/src/bridge/translator.rs	Adds fallback routing from React document language IDs to base server clients and tests for client selection.
CHANGELOG.md	Documents the fix under Unreleased.

[dergachoff]

Rebased onto main after v0.3.7. Two notes:

• The changelog entry moved under [Unreleased] and now carries the (#148) reference.
• get_client_for_file conflicted with feat(lsp): non-blocking startup for slow-to-initialize servers (large OmniSharp/Unity solutions) #173's ServerInitializing fallback. Resolved keeping both behaviors: exact client → React fallback client → ServerInitializing when the document language or its fallback server language is still initializing, else NoServerForLanguage.