fix(update): read model-page prices from a host that answers

End-to-end verification against the live site found the price capture broken for
a whole class of users: the civitai page hosts are not interchangeable, and the
user's civitai_host preference was silently fatal. With civitai_host=civitai.red
the update DB held zero prices even with tracking enabled.

- civitai.red refuses non-browser HTTP clients outright (Cloudflare challenge,
  403 for any User-Agent, aiohttp and httpx alike), while civitai.com and
  civitai.green answer normally for anonymously visible models and 404 for
  mature ones. An earlier manual check with curl passed on TLS fingerprint luck,
  which is why this was missed.
- get_model_prices now tries the configured host first, then the others, and
  takes the first parseable payload. The host that worked is remembered, and a
  host that refuses outright is parked for 15 minutes so a library full of
  mature models does not pay three requests each; a 404 is model-specific and
  does not park the host. Links keep using the configured host, which is where
  the user's own browser has clearance.
- Mature models still have no price source anywhere, so that is now stated
  instead of silent: price_check_attempted_at separates "tried and unreadable"
  from "never looked", gated versions show a muted "Price unavailable" badge,
  and the alerts panel reports unavailableCount.
- Failures are logged at warning level, once per host per TTL, with the
  per-host reason, instead of only at debug level.
- The recorded alternatives (internal tRPC with the user's API key, or an
  extension-assisted fetch from the user's browser) and the strengthened
  upstream ask for a public price field are documented in the plan.

tests/services/test_model_update_service.py

@@ -1884,3 +1884,74 @@ async def test_newest_price_checked_at_reports_the_latest_fetch(tmp_path):
 
     assert newest is not None
     assert newest > 0
+
+
+@pytest.mark.asyncio
+async def test_failed_price_attempt_is_recorded_as_unavailable(tmp_path):
+    """A gated version we tried to price and could not must be distinguishable
+    from one we never looked at — that is the honest "unavailable" state for
+    mature models, whose pages no host will serve anonymously."""
+
+    service = _price_service(tmp_path, price_tracking_enabled=True)
+    scanner = DummyScanner(LOCAL_RAW_DATA)
+    failing = PriceProvider(GATED_RESPONSE, prices=None)
+
+    await service.refresh_for_model_type("lora", scanner, failing)
+    record = await service.get_record("lora", 1)
+    version = next(v for v in record.versions if v.version_id == 12)
+
+    assert failing.price_calls == 1
+    assert version.price_buzz is None
+    assert version.price_checked_at is None
+    assert version.price_check_attempted_at is not None
+    assert service.count_unavailable_prices("lora") == 1
+    assert service.count_unavailable_prices("checkpoint") == 0
+    # Nothing to alert on, and no price alert state.
+    assert await service.get_price_alerts("lora") == []
+    assert version.price_alert_state is False
+
+
+@pytest.mark.asyncio
+async def test_successful_price_attempt_sets_both_markers(tmp_path):
+    service = _price_service(tmp_path, price_tracking_enabled=True)
+    scanner = DummyScanner(LOCAL_RAW_DATA)
+
+    await service.refresh_for_model_type(
+        "lora", scanner, PriceProvider(GATED_RESPONSE, prices=PRICE_PAYLOAD)
+    )
+    record = await service.get_record("lora", 1)
+    version = next(v for v in record.versions if v.version_id == 12)
+
+    assert version.price_buzz == 250
+    assert version.price_checked_at is not None
+    assert version.price_check_attempted_at is not None
+    assert service.count_unavailable_prices("lora") == 0
+
+
+@pytest.mark.asyncio
+async def test_no_price_attempt_is_recorded_while_tracking_is_off(tmp_path):
+    service = _price_service(tmp_path)  # tracking off
+    scanner = DummyScanner(LOCAL_RAW_DATA)
+
+    await service.refresh_for_model_type("lora", scanner, DummyProvider(GATED_RESPONSE))
+    record = await service.get_record("lora", 1)
+
+    assert record.versions[0].price_check_attempted_at is None
+    assert service.count_unavailable_prices("lora") == 0
+
+
+@pytest.mark.asyncio
+async def test_unavailable_marker_clears_when_the_version_becomes_free(tmp_path):
+    service = _price_service(tmp_path, price_tracking_enabled=True)
+    scanner = DummyScanner(LOCAL_RAW_DATA)
+
+    await service.refresh_for_model_type(
+        "lora", scanner, PriceProvider(GATED_RESPONSE, prices=None)
+    )
+    assert service.count_unavailable_prices("lora") == 1
+
+    await service.refresh_for_model_type("lora", scanner, DummyProvider(FREE_RESPONSE))
+    record = await service.get_record("lora", 1)
+
+    assert record.versions[0].price_check_attempted_at is None
+    assert service.count_unavailable_prices("lora") == 0