docs: initialize stub-service repo with ADR-001

Architecture Decision Record for a Go-based HTTP stub/mock service
(Mountebank alternative) with Web UI and LLM-powered config generation.

Covers: component architecture, technology choices (Go + chi + Templ/htmx
+ SQLite), API design, data model, deployment model.

.gitignore

@@ -0,0 +1,36 @@
+# Binaries
+stub-service
+*.exe
+*.dll
+*.so
+*.dylib
+
+# Build output
+/bin/
+/dist/
+
+# Test
+*.test
+*.out
+coverage.html
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Data
+/data/
+*.db
+*.db-wal
+*.db-shm
+
+# Environment
+.env
+.env.local