Consolidate: 65 decision records to 52

Jochen: a normal application has 3-5 ADRs, maybe 10 for a large one, and we are
at 65. Fair, and the cause is mine -- I recorded every FINDING as a decision
rather than every fork in the road.

Two merges, both cases where one decision had been split across many records
because it was taken over several days rather than at once.

0019 absorbs ten records about how this repository works: what it is and that
it is public, the folder flow, the two design layers, the issue front door,
status in frontmatter, playbooks, the naming rule, the product name. Those were
never ten decisions -- they were one, seen from ten angles as the repository
took shape.

0016 absorbs the five about the lab: a node is a virtual machine, a router is
scenery, a scenario declares the underlay, a scenario is a closed address
space, and the two scenario classes. Same pattern -- one design, split by the
order it was worked out in.

The consolidated 0019 also raises the bar for what earns a record, since that
is what produced 65: a record is warranted when there is a genuine fork -- a
direction reversed, an alternative that will be proposed again, something
contested. A finding is not a decision, and a bug is certainly not. Everything
else belongs in the design document where the reasoning is actually read.

The checker earned its place here. Deleting nine records left 13 dangling links
across the repository and it named every one, including in AGENTS.md. Nothing
was found by reading.

Remaining clusters worth the same treatment: the host (8 records), delivery
(5), modules (6), connectivity (4), substrate and control plane (4). That would
be 52 down to roughly 30.

02-DECISIONS/0041-the-host-depends-on-nothing.md

@@ -10,7 +10,7 @@ extends: 0037-the-host-applies-it-does-not-decide.md
 
 ## Context
 
-[ADR 0030](0030-the-repository-structure.md) calls tier 0 *"the one binary installed by hand"*,
+[ADR 0019](0019-how-this-repository-works.md) calls tier 0 *"the one binary installed by hand"*,
 and [research 006](../01-RESEARCH/006-mesh-from-scratch/00-overview.md) states the property the
 whole tier rests on: *"a binary whose whole argument is that it has no dependencies"*.
 
@@ -72,7 +72,7 @@ A second language usually costs duplicated logic; here there is none to duplicat
 
 ## References
 
-- [ADR 0030](0030-the-repository-structure.md) — *the one binary installed by hand*.
+- [ADR 0019](0019-how-this-repository-works.md) — *the one binary installed by hand*.
 - [ADR 0037](0037-the-host-applies-it-does-not-decide.md) — why the host shares no code.
 - [ADR 0039](0039-the-link-is-the-security-boundary.md) — why it receives declarations only.
 - [`05-the-node-host.md`](../03-DESIGN/01-to-be/05-the-node-host.md) — the design this serves.