fix: revert ADR edits and enforce immutable accepted records

Restore docs/adr to main; add check_adrs.py CI gate so existing ADR-*.md
files cannot be modified — supersede with a new numbered ADR instead.

docs/adr/ADR-0002-one-storage-format.md

@@ -6,13 +6,9 @@ Accepted (2026-07-08)
 
 ## Context
 
-Data lives across [storage floors](../00-glossary.md#t0--hot) T0–T4. Primary persistent
-stores are [T1](../00-glossary.md#t1--warm) (drone NVMe in flight) and
-[T3](../00-glossary.md#t3--warehouse) (ground warehouse after landing);
-[T0](../00-glossary.md#t0--hot) is the in-memory hot window,
-[T2](../00-glossary.md#t2--shared) optional on-board derived replication,
-[T4](../00-glossary.md#t4--dev) dev/sim slices. If each floor used a different
-format or layout, offload would need transformation code,
+Data lives in three places: on the drone's NVMe in flight (T1), in the ground
+warehouse after landing (T3), and in the dev/simulation environment. If each
+tier used a different format or layout, offload would need transformation code,
 schemas would drift, and a query proven on the bench would not run unchanged on
 flight data.