Release Pyxle Language Tools 0.3.1

[shivamsn97]

Cuts 0.3.1 from what is already on main: bumps the manifest and turns the CHANGELOG's Unreleased section into the release heading.

What ships

• The dev server is no longer interrupted seconds after it starts. 0.3.0 started it by typing into a shell terminal, and the Python extension's environment activation sends ^C first to interrupt whatever is running — killing the freshly started server. The extension owns the process now, so nothing else can write to it.
• Both debug configurations run the same environment: the React-browser flow used whatever pyxle came first on PATH, not VS Code's selected interpreter.
• A stale editable install is no longer refused — the pre-launch check asks what the interpreter can run, not what its package metadata claims — and a check that cannot answer lets the launch proceed instead of asserting pyxle is missing.
• The interpreter is visible and switchable from a .pyxl file (status-bar item + Pyxle: Select Python Interpreter), which is what made the version errors a dead end before.
• Five lifecycle gaps found in review: an async taskkill failure that could throw and strand the process tree on Windows, exit settling before stdio drained (printing "stopped" above the traceback), a dead onDidExit that cost a 120 s silent lockout when a server died on startup, a missing discovery re-check after the interpreter gate, and an over-claiming changelog line.

Patch, not minor — this exists to fix behaviour 0.3.0 shipped broken; the new status-bar affordance is part of that fix rather than a separate feature.

Verified: tsc --noEmit clean, 23/23 tests, and vsce package produces a clean 12-file / 110 KB .vsix carrying "version": "0.3.1" with no source, tests, tsconfigs or node_modules leaking in.