Port envd from e2b with internalized shared packages and Connect RPC

- Copy envd source from e2b-dev/infra, internalize shared dependencies
  into envd/internal/shared/ (keys, filesystem, id, smap, utils)
- Switch from gRPC to Connect RPC for all envd services
- Update module paths to git.omukk.dev/wrenn/{sandbox,sandbox/envd}
- Add proto specs (process, filesystem) with buf-based code generation
- Implement full envd: process exec, filesystem ops, port forwarding,
  cgroup management, MMDS integration, and HTTP API
- Update main module dependencies (firecracker SDK, pgx, goose, etc.)
- Remove placeholder .gitkeep files replaced by real implementations

envd/internal/api/cfg.yaml

@@ -0,0 +1,8 @@
+# yaml-language-server: $schema=https://raw.githubusercontent.com/deepmap/oapi-codegen/HEAD/configuration-schema.json
+
+package: api
+output: api.gen.go
+generate:
+  models: true
+  chi-server: true
+  client: false