Finish the Cairn OBS rename through services, docs, and assets

The rename commit before this one covered module paths and the obvious
user-facing strings; this is the rest of it -- the places where "sentry"
was a default value, a filename, or a picture rather than a word in a
sentence.

Defaults that changed: CLICKHOUSE_DATABASE (sentry -> cairnobs),
POSTGRES_DATABASE (sentry_metadata -> cairnobs_metadata), and
POSTGRES_USERNAME (sentry -> cairnobs), across api/alerting/ingest and
the enterprise binaries, plus the compose files and migrate scripts that
create those objects. These are *defaults*, so a deployment that sets
them explicitly is unaffected -- but any deployment relying on the old
defaults must have its environment updated before it picks this up, or
it will come up pointing at a database that doesn't exist.

Also: the light-mode logo variants (the dark ones existed alone, so the
landing page and sidebar rendered a dark mark on a light background),
regenerated favicons, and the docs/README/threat-model prose that still
said Sentry.

docs/compliance/license-inventory.json

@@ -8510,7 +8510,7 @@
     "direct_or_transitive": "direct",
     "ecosystem": "docker-image",
     "flagged": "True",
-    "flag_reason": "Category (c): BSL is explicitly source-available, not OSI-approved open source, per the audit's own classification framework. Verified against the actual licenses/bsl.md at the v24.2.7 tag, not assumed. No AGPL linking-compatibility issue (Redpanda is consumed only over the Kafka wire protocol, never linked into Sentry's own code -- same relationship as ClickHouse/Postgres). Real open question: whether a third party self-hosting Sentry (now fully AGPLv3 per task 6) 'as a service' would trip BSL's Streaming-or-Queuing-Service restriction on the bundled Redpanda image -- Sentry's ingest pipeline creates fixed internal topics, not per-end-user topics, so this is very likely NOT a Streaming-or-Queuing-Service under BSL's own definition, but this is a business/redistribution judgment call, not a pure technical one -- flagged for your decision, not resolved unilaterally. See license-audit-report.md's Redpanda section for the three remediation options (accept as-is / swap to Apache Kafka / flag only). RESOLVED 2026-08-16 (business decision): accept as-is. Sentry's own use (internal Kafka-protocol transport, no resale of broker access) is within BSL's Additional Use Grant; the third-party self-hosting-as-a-service question was judged unlikely to trip BSL's Streaming-or-Queuing-Service restriction, and was accepted as a known, disclosed risk rather than swapping to a heavier broker or dropping the bundled image. See license-audit-report.md's Redpanda section.",
+    "flag_reason": "Category (c): BSL is explicitly source-available, not OSI-approved open source, per the audit's own classification framework. Verified against the actual licenses/bsl.md at the v24.2.7 tag, not assumed. No AGPL linking-compatibility issue (Redpanda is consumed only over the Kafka wire protocol, never linked into Cairn OBS's own code -- same relationship as ClickHouse/Postgres). Real open question: whether a third party self-hosting Cairn OBS (now fully AGPLv3 per task 6) 'as a service' would trip BSL's Streaming-or-Queuing-Service restriction on the bundled Redpanda image -- Cairn OBS's ingest pipeline creates fixed internal topics, not per-end-user topics, so this is very likely NOT a Streaming-or-Queuing-Service under BSL's own definition, but this is a business/redistribution judgment call, not a pure technical one -- flagged for your decision, not resolved unilaterally. See license-audit-report.md's Redpanda section for the three remediation options (accept as-is / swap to Apache Kafka / flag only). RESOLVED 2026-08-16 (business decision): accept as-is. Cairn OBS's own use (internal Kafka-protocol transport, no resale of broker access) is within BSL's Additional Use Grant; the third-party self-hosting-as-a-service question was judged unlikely to trip BSL's Streaming-or-Queuing-Service restriction, and was accepted as a known, disclosed risk rather than swapping to a heavier broker or dropping the bundled image. See license-audit-report.md's Redpanda section.",
     "classification": "c"
   },
   {