Add gateway implementation planning docs

.gitignore

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+# OS files
+.DS_Store
+.DS_Store?
+._*
+Thumbs.db
+ehthumbs.db
+Desktop.ini
+$RECYCLE.BIN/
+
+# Editor and IDE state
+.vs/
+.vscode/*
+!.vscode/extensions.json
+!.vscode/launch.json
+!.vscode/settings.json
+!.vscode/tasks.json
+.idea/
+*.suo
+*.user
+*.userosscache
+*.sln.docstates
+*.rsuser
+*.DotSettings.user
+
+# Local environment and secrets
+.env
+.env.*
+!.env.example
+*.local
+*.secret
+*.secrets
+secrets.json
+
+# Logs and crash dumps
+*.log
+logs/
+*.dmp
+*.dump
+*.mdmp
+
+# Build artifacts
+artifacts/
+dist/
+build/
+out/
+tmp/
+temp/
+
+# .NET
+**/bin/
+**/obj/
+TestResults/
+*.trx
+*.coverage
+*.coveragexml
+coverage/
+packages/
+*.nupkg
+*.snupkg
+project.lock.json
+project.assets.json
+*.nuget.props
+*.nuget.targets
+
+# Go
+clients/go/bin/
+*.test
+coverage.out
+coverage.html
+go.work.sum
+
+# Rust
+target/
+**/target/
+*.profraw
+
+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+.Python
+.venv/
+venv/
+env/
+ENV/
+.pytest_cache/
+.ruff_cache/
+.mypy_cache/
+.pyre/
+.tox/
+.nox/
+.coverage
+.coverage.*
+htmlcov/
+pip-wheel-metadata/
+*.egg-info/
+*.egg
+
+# Java, Maven, and Gradle
+.gradle/
+**/target/
+**/build/
+*.class
+*.jar
+!**/gradle/wrapper/gradle-wrapper.jar
+*.war
+*.ear
+*.nar
+hs_err_pid*
+replay_pid*
+
+# Node tooling, used by frontend or documentation tools if added
+node_modules/
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+.parcel-cache/
+.next/
+.nuxt/
+.svelte-kit/
+
+# Protobuf and generated build scratch
+*.protobin
+*.protodesc
+*.pb.tmp
+generated-scratch/
+
+# Local database and service state
+*.db
+*.db-shm
+*.db-wal
+*.sqlite
+*.sqlite3
+*.bak
+*.ldf
+*.mdf
+
+# Archives and packages produced locally
+*.zip
+*.7z
+*.tar
+*.tar.gz
+*.tgz
+*.rar
+
+# Keep empty directories with .gitkeep files when needed
+!.gitkeep