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.

02-DECISIONS/README.md

@@ -92,7 +92,6 @@ python3 00-META/checks/index.py            fail if stale
 - **0006** — [The substrate and the control plane](0006-the-substrate-and-the-control-plane.md)
 - **0007** — [Connectivity](0007-connectivity.md)
 - **0008** — [A context owns its store, exclusively](0008-a-context-owns-its-store.md)
-- **0024** — [Running the control plane](0024-running-the-control-plane.md)  *(proposed)*
 
 ### What runs on them, and how it gets there