Initial scoping: architecture + Asterisk→Rust port plan

Establish rutster — a memory-safe, API-first, security-first telephony
platform; spiritual successor to Asterisk for the WebRTC/microservices era.

- README: project framing, design pillars, open decisions
- docs/ARCHITECTURE.md: three-plane (control/media/app) model
- docs/PORT_PLAN.md: every Asterisk subsystem mapped to a disposition
  (core / WASM-plugin / service / edge-FFI / dropped / replaced) with rationale

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01C2bfD7MkqEdfnMXxXBu456

.gitignore

@@ -0,0 +1,19 @@
+# Rust
+/target
+**/target
+**/*.rs.bk
+*.pdb
+
+# Cargo.lock is committed (this is an application workspace, not a library)
+
+# Env / secrets
+.env
+.env.*
+*.pem
+*.key
+
+# Editor / OS
+.DS_Store
+*.swp
+.idea/
+.vscode/