Add Theia base + Product OS vision and guides

Co-authored-by: Cursor <cursoragent@cursor.com>

.gitignore

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+# Theia build files
+theia/node_modules/
+theia/packages/*/lib/
+theia/examples/*/lib/
+theia/examples/*/dist/
+theia/*.log
+theia/.nyc_output/
+theia/coverage/
+theia/lerna-debug.log*
+theia/npm-debug.log*
+
+# OS files
+.DS_Store
+.DS_Store?
+._*
+.Spotlight-V100
+.Trashes
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+
+# Temporary files
+*.tmp
+.cache/
+
+# Distribution builds
+theia/examples/electron/dist/
+
+# Environment
+.env
+.env.local