Spotnet import, header backfill, staging and counter grouping, faster search

Spotnet (CONCEPT D29):
- Index free.pt fully and import spots with their descriptions, categories
  and NZBs; a spot renames its release, since Spotnet names are more
  trustworthy than names derived from subjects.
- Find passwords in spot descriptions too, and tell "needs a password we
  have" from "needs a password we don't have".

Content inspection:
- List the contents of 7z (.7z.001) archives, SFV sets, nicovideo uploads
  and other archive-like files; mark yEncBin .bin containers as encrypted.
- Take real names from yEnc headers for randomly named files, and merge
  uploads that were split across posts.

Storage (D31, D32):
- Store segment lists zstd-compressed behind the FileStore accessor.
- group:backfill indexes older headers at low priority and pauses when
  the NVMe or HDD part of the database gets too large.

Grouping (D35, D36):
- Lone header segments wait in staged_segments until a second segment of
  their file arrives, which drops the per-article junk binaries.
- Counter grouping joins random-subject uploads by poster, [i/M] counter,
  part count and day.

Search and maintenance (D33, D34):
- A trigram-indexed search_text column, smaller indexes, estimated stats.
- Passes that clean up nonsense names; weekly index maintenance; GC budgets
  per kind.
- Web UI: grey out stale results while a search runs and cancel superseded
  requests. Count only up to 1,000 matches for the page, which made filter
  clicks take seconds (Newznab keeps the 10,000 cap).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/nntp/date_search.ts

@@ -0,0 +1,27 @@
+/**
+ * The article number where a group's posts reach `target` (ms since epoch),
+ * by binary search between `first` and `last`. Article numbers only roughly
+ * follow posting time, so the answer is within `precision` articles of the
+ * first one posted at or after `target`.
+ *
+ * `dateOf(n)` returns the posting time of the first article at or after `n`
+ * that still exists, or null when there is none nearby (expired or removed);
+ * a gap counts as older than `target`.
+ */
+export async function articleAtDate(
+  first: bigint,
+  last: bigint,
+  target: number,
+  dateOf: (n: bigint) => Promise<number | null>,
+  precision = 10_000n
+): Promise<bigint> {
+  let lo = first
+  let hi = last
+  while (hi - lo > precision) {
+    const mid = lo + (hi - lo) / 2n
+    const date = await dateOf(mid)
+    if (date === null || date < target) lo = mid
+    else hi = mid
+  }
+  return lo
+}