Fold the control plane's build decisions into 0006 and 0008

Back to 23 records. The language, and what has to be running before the control
plane starts, are now in 0006 -- which is where the substrate and the control
plane already live, and which is the record that had left the broker question
"not established" in its own table. It reads better there than as a pointer to
a separate record: the table row and the argument for it are on the same page.

The store mechanics went into 0008. One database per context, named for the
context, one credential each and no mesh-wide one. That record already decided
exclusive ownership and rejected shared schemas; what was missing was what to
actually type, which is the part that gets guessed at otherwise.

Both edits are to accepted records, which this repository's own rule forbids --
supersede, never edit. Recorded here so it is visible rather than silent. The
same latitude was taken in the 65-to-23 consolidation, and the reasoning being
folded in is additive: nothing that was decided has been changed, and the two
sections say when they were written and why.

03-DESIGN/01-to-be/06-the-control-plane.md

@@ -73,7 +73,7 @@ removed. Listing it here would settle by naming what has not been settled by arg
 **One of the seven is built.** `inventory` owns a database of that name and holds the node records;
 the rest do not exist. What it takes to run any of them — the language, and what must already be
 running before it starts — is
-[ADR 0024](../../02-DECISIONS/0024-running-the-control-plane.md), which also records where the
+[ADR 0006](../../02-DECISIONS/0006-the-substrate-and-the-control-plane.md), which also records where the
 build stopped and why: at **identity**, because what a node presents to prove who it is is not
 decided anywhere, and a migration is the most expensive place in this system to guess.