Order the records the way the system is learned

Jochen asked whether the order made sense. It did not -- it followed when
things happened to be decided, which after consolidation is fictional anyway
since record 5 alone folds decisions taken across a week.

Concretely wrong before: the domain statement sat at 8, after five engineering
rules; the constitution was scattered across 5, 12 and 17; the tiers landed at
15, 16, 21 and 22 with process records in between.

Now it walks: what the mesh is (1-3), its tiers from the bottom up (4-8), what
runs on them and how it gets there (9-10), how it is built (11-16), how it is
checked (17-18), how we work (19-23).

Two things made this safe rather than free. It is a permutation, not a
compaction, so the renames go through temporary names -- otherwise two files
want one slot and one is lost. And the reference rewrite is a single
simultaneous pass, because almost every number moved into a slot another number
was vacating; replacing one at a time would have cascaded and pointed things at
the wrong record while still resolving.

Verified: 284 [ADR NNNN](path) links across the repository, all with matching
text and target.

The ordering principle is now stated in 19 rather than left implicit -- the
repository already said "the numbering is the flow" about its folders, and
there was no reason for the records to be the exception.

02-DECISIONS/README.md

@@ -15,7 +15,7 @@ The records run in the order the decisions were taken, oldest first.
 
 **Every decision is a record.** There is no ledger and no index file — if a decision is worth
 recording it is worth a record, and if it is not worth a record it is not recorded
-([ADR 0011](0011-how-this-repository-works.md)). A "decision" small enough to be one line is
+([ADR 0019](0019-how-this-repository-works.md)). A "decision" small enough to be one line is
 almost always a **rule**, and a rule belongs in
 [`00-META/how-we-build.md`](../00-META/how-we-build.md), where it is enforced and keeps the
 incident that earned it.