Initial boilerplate scaffold for continuum-common

Adds ts-core (logger, Supabase JWT verification, Elysia error
transformers) and rust-core (thiserror error type, tracing init,
G-code checksum/header parsing) packages.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,20 @@
+# Node / Bun
+node_modules/
+dist/
+*.tsbuildinfo
+bun.lockb
+.bun/
+
+# Rust
+target/
+Cargo.lock
+
+# Env
+.env
+.env.local
+
+# Editors / OS
+.DS_Store
+.vscode/
+.idea/
+*.log