cerebellum: plug-and-play OpenHermes harness on the Ichor bus

C1 integration spine as an Ichor organ. CerebellumHarness receives a turn off
the bus, sequences N passes through a swappable LLM adapter (the OpenHermes
plug; StubLLM stands in), and emits the synthesis back onto the bus toward the
Brain (crossing D1). Add Cerebellum to OrganId; wire a turn in the demo main.
Compiles on ponyc 0.64; end-to-end run green (turn -> cerebellum -> D1 -> brain).

Also: add a small read-only permission allowlist (toolchain probes/versions).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015hmgREHNsxYCuim33yUF2c

src/ichor/envelope.pony

@@ -9,7 +9,7 @@ Envelope is `class val`: immutable and sendable between actors.
 """
 
 type OrganId is
-  ( DriveBox | EnergyTorus | Soul | Metacog | Brain
+  ( DriveBox | EnergyTorus | Soul | Metacog | Brain | Cerebellum
   | AdaBorder | Storage | MiniRag | UnknownOrgan )
 
 primitive DriveBox
@@ -22,6 +22,8 @@ primitive Metacog
   fun string(): String => "metacog"
 primitive Brain
   fun string(): String => "brain"
+primitive Cerebellum
+  fun string(): String => "cerebellum"
 primitive AdaBorder
   fun string(): String => "ada_border"
 primitive Storage