World folder is the source of truth

- actor/<id>/ holds actor.wasm, actor.json, source/, public/, data/, versions/
- the broker boots by scanning actor/; a changed actor.wasm is an upgrade,
  a rejected one stays in versions/ with a reason and the files come back
- /actor hides every data/ folder
- subscriptions live in the subscriber's actor.json
- cargo installs the SDK and points sausage-actor at it; no build limits
- PROTOCOL.md

Cargo.lock

@@ -1593,6 +1593,7 @@ dependencies = [
  "serde",
  "serde_json",
  "tokio",
+ "toml_edit",
  "wasmtime",
  "wasmtime-wasi",
  "wasmtime-wasi-http",
@@ -1933,6 +1934,19 @@ dependencies = [
  "serde_core",
 ]
 
+[[package]]
+name = "toml_edit"
+version = "0.25.17+spec-1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e3641d5bbb5349a79e1020a242d251efbc546ad8048d133958323ce9c40a9c9c"
+dependencies = [
+ "indexmap",
+ "toml_datetime",
+ "toml_parser",
+ "toml_writer",
+ "winnow",
+]
+
 [[package]]
 name = "toml_parser"
 version = "1.1.5+spec-1.1.0"
@@ -2795,6 +2809,9 @@ name = "winnow"
 version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "23b97319f7b8343df12cc98938e5c3eb436064524c8d2b4e30a1d3a36eecdf81"
+dependencies = [
+ "memchr",
+]
 
 [[package]]
 name = "winx"