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

README.md

@@ -47,7 +47,7 @@ own resolved environment.
 - **A module's API client and its tool implementations** → in the module. (The Plex client, the
   Umami client, `tools/plex.ts` — all module-local. ADR 0039.)
 - **Delivery machinery** — build executor, bundler, dependency resolver, artifact manager, feature
-  handlers → **mesh-control**. It co-evolves with the pipeline.
+  handlers → **mesh-controller**. It co-evolves with the pipeline.
 - **Host synchronisers** — config-sync, ufw config, vhost generation, systemd, health checks →
   **mesh-host**'s apply engine. The host applies these; they are not module code.
 - **Domain logic** — tasks, workflows, agents, provider integrations → **tier-2 contexts**.