v3.7 Pass 3b: clarify DATA organ — volume is ReadWrite, sealed-ness is application-level

data-loop.md Instance Lifecycle intro now pre-empts the apparent tension
between a ReadWriteMany DATA volume and sealed/append-only instance
semantics. Adds one short paragraph: the volume permits writes; the
platform enforces write-once-per-file and append-only ledgers at the
write boundary — not via volume-level restrictions. Closes the last
Priority-3 Pass 0 touch-up (task #22).

No other content changes.

Author: styk-tv

docs/v3.7/data-loop.md

@@ -127,6 +127,8 @@ Conformant implementations MUST publish the following NATS topics for DATA loop
 
 ## Instance Lifecycle -- Create, Seal, Ledger
 
+The DATA volume is mounted ReadWriteMany (the kernel can create new instance folders, append ledger entries, and write proof records). The *sealed* and *append-only* semantics below are application-level contracts the platform enforces at the write boundary — not volume-level restrictions. Rephrased: the volume permits writes; the platform ensures each sealed file is written exactly once and each ledger is extended (not rewritten).
+
 Instance lifecycle follows a strict progression:
 
 ```mermaid