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.

docs/adr/ADR-0003-sync-derived-state-only.md

@@ -0,0 +1,33 @@
+# ADR-0003: Sync derived state only; raw telemetry stays local
+
+## Status
+
+Accepted (2026-07-08)
+
+## Context
+
+Each drone produces high-rate sensor telemetry and on-board video detections —
+far more than the mesh can carry. But peers only need enough to coordinate
+flight: where everyone is, where they are heading, what was detected. Pushing
+raw feeds across the air would saturate the radio and drain batteries for data
+nobody reads in flight.
+
+## Decision
+
+Only **derived state** crosses the air — position, attitude, detections — as
+small pub/sub broadcasts (~5 Hz). **Raw telemetry stays on local NVMe** until
+the drone lands, then travels to the warehouse during offload
+([ADR-0002](ADR-0002-one-storage-format.md)). The design is **event-driven**:
+new derived data triggers downstream action through hooks; nothing polls asking
+"anything new yet?".
+
+## Consequences
+
+- Air bandwidth scales with the number of peers and the broadcast rate, not
+  with sensor resolution.
+- The warehouse is the only place with the full picture; in-flight decisions use
+  the local window plus peer broadcasts.
+- Broadcast staleness per peer becomes a first-class health signal
+  ([`../07-observability.md`](../07-observability.md)).
+- What syncs and what does not is specified in
+  [`../04-swarm-sync.md`](../04-swarm-sync.md).