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- Web UI: grey out stale results while a search runs and cancel superseded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>

tests/unit/date_search.spec.ts

@@ -0,0 +1,14 @@
+import { test } from '@japa/runner'
+import { articleAtDate } from '#lib/nntp/date_search'
+
+test.group('nntp / articleAtDate', () => {
+  test('finds the article posted at a time, skipping gaps', async ({ assert }) => {
+    // One article a second from t0, articles 1,000,000–1,100,000; 1,040,000–1,040,999 expired.
+    const t0 = Date.UTC(2026, 8, 1)
+    const dateOf = async (n: bigint) => (n >= 1_040_000n && n < 1_041_000n ? null : t0 + Number(n - 1_000_000n) * 1000)
+    const at = await articleAtDate(1_000_000n, 1_100_000n, t0 + 60_000 * 1000, dateOf, 100n)
+    assert.isAtLeast(Number(at), 1_059_900)
+    assert.isAtMost(Number(at), 1_060_000)
+    assert.equal(await articleAtDate(1_000_000n, 1_100_000n, t0 - 1, dateOf, 100n), 1_000_000n)
+  })
+})