Per-system bundles, and Android's start problem closed by narrowing it

Two gaps.

The bundle's contents are per system even though its mechanism is not, so there
are now three: substrate-arch.lock, substrate-alpine.lock and
substrate-android.lock. All three are embedded and a host reads only the one it
was built for. Arch and Alpine remain placeholders -- the closure for a one-node
mesh is still research 011/012's open question, and inventing it here would be
worse than an honest placeholder.

Android's is not a placeholder. It says a partial host cannot raise a mesh and
why: every step of a bootstrap is a package, a container, or an action against
one, and those are exactly the shapes it refuses. So a partial host can JOIN a
mesh and cannot BE the first node. That belongs where somebody looking for the
android bundle will find it.

Also separated two things that were being conflated: "this system has no
bundle" and "this system was never built". Loading a bundle for debian is not
ErrEmpty, and the test asserts they differ.

0062 -- a host may be episodic. There is no way to keep a process running on an
ordinary Android device: init needs root, a foreground service can be killed
for memory. The answer is not to fight that. It is that being killed IS
disconnection, which ADR 0036 already made an ordinary situation -- and
everything the design does for a laptop that closes is what an episodic host
needs, at a shorter period. An authoritative local store, reconcile on start,
last-heard-from reported without an alarm.

So the gap closes by requiring less rather than building something. No keep-
alive, no Android daemon, no fighting the platform's process management.

Two consequences recorded rather than glossed. Last-heard-from is a much weaker
signal on an episodic host, so a healthy phone reads as a dead server unless
the reader knows which kind it is looking at. And a declaration may take a long
time to land, which makes 0058's separation of outstanding from failed
load-bearing rather than tidy.

Left open deliberately: how an episodic host is actually started, and -- first --
what an Android node is for. Building the start mechanism before deciding that
would be building it for nobody.

internal/bundle/substrate-android.lock

@@ -0,0 +1,12 @@
+// substrate-android.lock — deliberately not a bundle.
+//
+// An android host cannot raise a mesh, and this file says so rather than being an empty
+// placeholder waiting to be filled in.
+//
+// The substrate is a container runtime, a store and the control plane (novox/hq
+// 07-the-substrate.md). An android host implements `file`, `directory` and `action` and refuses
+// `package`, `container` and `service` (ADR 0060) — so every step of the bootstrap is a shape it
+// does not have. No amount of filling this in changes that.
+//
+// **A partial host can JOIN a mesh and cannot BE the first node.** That is a real distinction
+// and it belongs here, where somebody looking for the android bundle will find it.