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>

README.md

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+# continuum-common
+
+Shared, dependency-light building blocks used across the Continuum cloud and edge services.
+
+## Packages
+
+- **`packages/ts-core`** — TypeScript package consumed by `continuum-backend` (and other Bun/Node services). Provides a structured logger, a Supabase JWT verification helper, and ElysiaJS-compatible HTTP error transformers.
+- **`packages/rust-core`** — Rust crate consumed by `continuum-proxy` and `continuum-ai-worker`. Provides a shared `thiserror`-based error type, `tracing` initialization, and G-code checksum/header parsing helpers.
+
+Each package is versioned and published independently; see their own READMEs (inline doc comments) for usage.