Rename mesh-control -> mesh-controller, substrate -> foundation

One name per thing, per the HQ glossary: the module/container/image/binary/repo
becomes mesh-controller, the seat the-controller, and the store+broker pair the
foundation (embedded base bundles, default template and example lock renamed with
their go:embed directives). No behaviour change — a pure vocabulary rename.

Claude-Session: https://claude.ai/code/session_01D6qtiYU3P9jk3pnAXyAFyx

test/supported.test.ts

@@ -60,20 +60,20 @@ place: { all: [host] }`);
 });
 
 test("a tier above 0 is still refused, and named", () => {
-  // The refusal narrowed rather than disappearing. A scenario placing a host AND a substrate
+  // The refusal narrowed rather than disappearing. A scenario placing a host AND a foundation
   // must be told which half is missing — not that `place:` is unsupported, when half of it
   // now works.
   const scenario = parseScenario(`scenario: x
 segments: { net: { kind: public, cidr: [192.0.2.0/24] } }
 machines: { a: { at: { segment: net, address: [192.0.2.1] } } }
-place: { all: [host, substrate] }`);
+place: { all: [host, foundation] }`);
   try {
     assertSupported(scenario);
     assert.fail("should have refused");
   } catch (err) {
     assert.ok(err instanceof UnsupportedError);
-    assert.equal(err.missing.length, 1, `expected only the substrate: ${err.missing.join(", ")}`);
-    assert.match(err.missing[0] ?? "", /substrate/);
+    assert.equal(err.missing.length, 1, `expected only the foundation: ${err.missing.join(", ")}`);
+    assert.match(err.missing[0] ?? "", /foundation/);
     assert.match(err instanceof Error ? err.message : "", /silently lacks them/);
   }
 });