feat(v2): nostr-transport roster-resolver hook (#20 path-B)

Exposes `resolve(sender_pubkey_hex) -> RouteHit | None` and a
`register_with_lnbits()` helper that lazily-imports + soft-fails on
lnbits versions without `register_roster_resolver`. Wired into
`satmachineadmin_start()`.

The hook delivers the path-B outcome ("cash-out sats go to the
operator's wallet, not an auto-created machine wallet") once the
lnbits side ships its half. Shape contract `(operator_user_id,
wallet_id, source_extension)` frozen per coord-log 2026-05-31T15:25Z.
Branch held local until lnbits lands the registry — no behaviour
change on the current lnbits version, just the future-ready handoff
+ a benign INFO log on boot.

Boot-smoked in dev container: extension loads, registration logs the
documented soft-fail message, invoice listener + cassette consumer
unchanged. 6 new unit tests cover happy path, miss, bech32 +
uppercase canonicalisation, fail-closed on malformed input, and the
soft-fail register branch.

nostr_transport_roster.py

@@ -15,7 +15,7 @@ registration call lazily-imports + soft-fails so satmachineadmin keeps
 loading cleanly on any lnbits version.
 
 When the lnbits implementation lands + the satmachine instance has
-`NOSTR_TRANSPORT_ROSTER_REQUIRED=true` set, inbound kind-21000
+`LNBITS_NOSTR_TRANSPORT_ROSTER_REQUIRED=true` set, inbound kind-21000
 RPCs from a registered ATM npub will route directly to the operator's
 wallet (delivering the "cash-out sats go to the operator's wallet, not
 an auto-created machine wallet" outcome). Unregistered npubs get
@@ -138,6 +138,6 @@ def register_with_lnbits() -> bool:
         "resolver with lnbits nostr-transport — inbound kind-21000 "
         "from a registered ATM npub will route to the operator's wallet "
         "directly. (Behavior gated server-side by "
-        "NOSTR_TRANSPORT_ROSTER_REQUIRED.)"
+        "LNBITS_NOSTR_TRANSPORT_ROSTER_REQUIRED.)"
     )
     return True