Update trace-target references for the relocated rendezvous modules

Moving the nostr rendezvous engine to src/nostr/ (and mDNS to src/mdns/)
changed the module-path-derived tracing targets from
fips::discovery::nostr::* to fips::nostr::*. Update the RUST_LOG filters
in the NAT and mesh-lab test compose files and the resolve-peers-via-nostr
tutorial's debug recipe to the new targets so trace configs and the
documented journal-watch command keep emitting the intended lines.

Without this, the stun-faults suite's Phase-0 pre-flight (which greps the
daemon journal for the debug-level "STUN observation succeeded" /
"traversal: initiator STUN observed" lines) saw those lines suppressed —
the daemon behaved correctly, but the stale RUST_LOG target hid the
evidence. Test-harness and docs only; no source or behavior change.

docs/tutorials/resolve-peers-via-nostr.md

@@ -178,7 +178,7 @@ The resolution itself happens at debug-log level, so you will
 not see it in the default-level journal. The user-facing way to
 confirm everything worked is `fipsctl show peers` in the next
 step. (To watch the resolution in the journal, run the daemon
-manually with `RUST_LOG=fips::discovery::nostr=debug`; not
+manually with `RUST_LOG=fips::nostr=debug`; not
 necessary for this tutorial.)
 
 ## Step 5: Verify the resolved endpoint