chore(vscode-extension): .vscodeignore + 0.2.0 .vsix artefact

Adds the missing `.vscodeignore` so future `vsce package` runs don't
bundle the webview's `node_modules/` (which made the v0.1.0 release
17 MB instead of <1 MB — webview is a thin React WebView app that
ships only its compiled bundle).

With the ignore in place, 0.2.0 packages down to 100 KB (10 files:
extension.js + webview index.js + manifest + LICENSE + README +
changelog + icon + diagram schema). Matches the precedent of
committing the .vsix alongside the source for offline installation.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

vscode-extension/.vscodeignore

@@ -0,0 +1,31 @@
+# Source we don't need at runtime — the bundled dist/extension.js is the
+# only entry point. Webview ships its compiled dist/ but not its sources.
+.git/**
+.github/**
+.vscode/**
+.vscode-test/**
+src/**
+node_modules/**
+
+webview/src/**
+webview/node_modules/**
+webview/package*.json
+webview/tsconfig.json
+webview/vite.config.ts
+webview/index.html
+
+# Build + dev artefacts
+**/*.ts
+**/*.map
+**/tsconfig.json
+**/.eslintrc*
+.gitignore
+.npmignore
+.editorconfig
+
+# Project-level docs that aren't user-facing
+CONTRIBUTING.md
+DEVELOPMENT.md
+
+# Previously-published artefacts
+*.vsix