docs: record architecture decisions (ADR-0001..0009) and operations knowledge

Add docs/adr/ with a chronological ADR set reconstructed from the project
history (no orchestrator, one storage format, derived-state sync,
SQL-over-SSH contract, WireGuard beneath SSH, IaC boundaries, non-root
image, runtime data paths, bounded lake scans), an index README, and a
template. Distinguish repo-local ADRs from ecosystem-wide ASRs.

Expand AGENTS.md with a decision-records section and a runtime/operations
guide (service URLs, rebuild workflow, CPU budget knobs). Reference the
ADRs from README, CONTRIBUTING, and the affected design docs, and add an
open question for T1 partition pruning.

README.md

@@ -33,6 +33,9 @@ This repository describes how to build, deliver, test, and operate that platform
 | [09 — Open questions](docs/09-open-questions.md) | Known unknowns and proposed answers |
 | [10 — Domain context](docs/10-domain-context.md) | Swarm autonomy principles this design builds on |
 | [11 — CI/CD & delivery](docs/11-cicd-delivery.md) | Pipelines, registry, dev containers, fleet releases |
+| [ADRs](docs/adr/) | Architecture Decision Records — the decisions behind the above, in the order they were made |
+
+The design principles below are the *what*; the [ADRs](docs/adr/) are the *why and when* — each principle traces to a dated, immutable decision record.
 
 ## Runnable parts