fix(cli/tests/dm): bind relay to 127.0.0.2 + dm-06 → --since filter

Two fixes needed to make the DM harness actually pass end-to-end:

1. Bind the loopback relay to 127.0.0.2 instead of 127.0.0.1.

   Quartz's `RelayTag.parse` (called from `ChatMessageRelayListEvent.
   relays()`) rejects any URL for which `isLocalHost()` returns true —
   the substring check matches `"127.0.0.1"` among others. That means a
   kind:10050 event whose `relay` tag reads `ws://127.0.0.1:8090/`
   silently parses to an empty relay list, and `RecipientRelayFetcher`
   reports `dmInbox == []`. Under strict mode `dm send` then correctly
   refuses with `no_dm_relays` — hiding an otherwise-valid test setup.

   `127.0.0.2` is the cleanest fix: still pure loopback (no network
   traffic, no config needed), not matched by `isLocalHost()`, and
   Linux binds any IP in 127.0.0.0/8 without setup. The Marmot harness
   is unaffected because its tests never depend on parsing their own
   kind:10051/10002 relay tags back out — they hit the bootstrap
   fallback path.

   marmot/setup.sh's `start_local_relay` now reads `${RELAY_HOST:-
   127.0.0.1}` so both harnesses can share it; the DM harness sets
   `RELAY_HOST=127.0.0.2` by default and exposes `--host` as an escape
   hatch.

2. Replace dm-06 cursor-advance check with `--since` filter check.

   The original assertion ("second no-flag `dm list` returns 0") was
   wrong for the actual design: `filterGiftWrapsToPubkey` always
   subtracts a 2-day lookback from `since` (required to catch NIP-59's
   randomised `created_at`), so a repeat no-flag query legitimately
   re-pulls everything in the last two days. The cursor advances the
   scan window for efficiency, not for idempotency. dm-06 now verifies
   `--since` actually filters: query with `--since <newest + 2 days +
   1 hour>` — after the filter's lookback subtraction, the effective
   floor lands past every message, and the list comes back empty.

Also: added `protoc` to the DM preflight checks so the missing-dep
error comes before 4 failed cargo retries.

Result on this machine: 6/6 pass, two clean runs in a row.

cli/tests/dm/dm-interop-headless.sh

@@ -27,11 +27,16 @@ AMY_BIN="$REPO_ROOT/cli/build/install/amy/bin/amy"
 # Share the nostr-rs-relay checkout with the Marmot harness to avoid
 # rebuilding it twice. Override RELAY_REPO / RELAY_DATA if you want full
 # isolation between runs.
+# Bind the loopback relay to 127.0.0.2 rather than 127.0.0.1 so Quartz's
+# `isLocalHost()` filter doesn't silently strip it out of the kind:10050
+# inbox events during recipient-relay resolution. 127.0.0.2 is still pure
+# loopback — no network traffic, no config needed.
+RELAY_HOST="${RELAY_HOST:-127.0.0.2}"
 RELAY_REPO="${RELAY_REPO:-$TESTS_DIR/marmot/state-headless/nostr-rs-relay}"
 RELAY_BIN="$RELAY_REPO/target/release/nostr-rs-relay"
 RELAY_DATA="$STATE_DIR/relay"
 RELAY_PORT="${RELAY_PORT:-8090}"
-RELAY_URL="ws://127.0.0.1:$RELAY_PORT"
+RELAY_URL="ws://$RELAY_HOST:$RELAY_PORT"
 NO_BUILD=0
 
 A_NPUB=""
@@ -41,7 +46,8 @@ D_HEX=""
 
 while [[ $# -gt 0 ]]; do
   case "$1" in
-    --port)     RELAY_PORT="$2"; RELAY_URL="ws://127.0.0.1:$RELAY_PORT"; shift ;;
+    --port)     RELAY_PORT="$2"; RELAY_URL="ws://$RELAY_HOST:$RELAY_PORT"; shift ;;
+    --host)     RELAY_HOST="$2"; RELAY_URL="ws://$RELAY_HOST:$RELAY_PORT"; shift ;;
     --no-build) NO_BUILD=1 ;;
     -h|--help)
       sed -n '3,12p' "${BASH_SOURCE[0]}" | sed 's/^# \?//'
@@ -97,4 +103,4 @@ test_02_dm_list_surfaces_history
 test_03_dm_send_rejects_no_inbox
 test_04_dm_send_allow_fallback
 test_05_dm_file_reference_round_trip
-test_06_dm_list_cursor_advance
+test_06_dm_list_since_filter