Bucketeer UI (dark mode, pagination, virtual scroll), readable+indexed resources, LLM-friendly logs

Logging:
- structured slog with LOG_FORMAT=json|text and a stable key vocabulary
- periodic stats record with queue depths, db pool, goroutines, memory, dns/probe
- no per-certificate logging (hot path is counters only)

UI (Bucketeer branding, DESIGN.md):
- light+dark themes (OS default, persisted header toggle, no first-paint flash)
- official mascot: lossless WebP light/dark logos + favicon, embedded and served
  with cache headers (1.2MB source PNGs -> ~27/22KB webp)
- Assets/Contents views, pagination (offset) and native virtual scrolling
  (content-visibility) so large result sets do not blow up the DOM
- search with debounce/abort + URL state, exposure chips, sort, summary counts

Readability + indexing:
- internal/index listers for S3-compatible, GCS, Azure, Firebase, OpenSearch
  (metadata only: keys/sizes/dates; never object contents)
- asset_entries table + store write/search; readable resources are indexed and
  searchable in the UI
- deep, unauthenticated, read-only DB probes (PROBE_DEEP): Redis PING,
  PostgreSQL StartupMessage, MongoDB OP_MSG listDatabases; OpenSearch/Neptune
  HTTP reads
- Azure account-level listing fixed: 403 is reported reachable, not
  auth_required, since anonymous access is per-container

DNS:
- curated reliable resolvers by default; DNS_SERVERS=fresh adds the compiled-in
  Fresh-Resolvers snapshot with a bounded startup sample (warming all 6.7k at
  once broke the container resolver)
- random healthy selection + failover + per-server cooldown

Other: prober Close fixes a shutdown hang; config/README updated.

migrations/0001_schema.sql

@@ -39,6 +39,24 @@ CREATE TABLE IF NOT EXISTS observations (
 
 CREATE INDEX IF NOT EXISTS observations_asset_idx ON observations (asset_id, observed_at DESC);
 
+-- Metadata index of resources confirmed anonymously readable. Keys/sizes/dates
+-- only; never object contents.
+CREATE TABLE IF NOT EXISTS asset_entries (
+    id           BIGSERIAL PRIMARY KEY,
+    asset_id     BIGINT      NOT NULL REFERENCES cloud_assets (id) ON DELETE CASCADE,
+    kind         TEXT        NOT NULL,
+    name         TEXT        NOT NULL,
+    size         BIGINT      NOT NULL DEFAULT 0,
+    updated      TIMESTAMPTZ,
+    content_type TEXT        NOT NULL DEFAULT '',
+    etag         TEXT        NOT NULL DEFAULT '',
+    indexed_at   TIMESTAMPTZ NOT NULL DEFAULT now(),
+    UNIQUE (asset_id, kind, name)
+);
+
+CREATE INDEX IF NOT EXISTS asset_entries_asset_idx ON asset_entries (asset_id);
+CREATE INDEX IF NOT EXISTS asset_entries_name_idx ON asset_entries (name);
+
 -- CT resume state. `state` is the JSON-encoded certspotter monitor.LogState
 -- (download/verified Merkle positions and last verified STH). No certificate
 -- contents are ever stored here.