feat(sources): fetch linked URLs for the 252 spreadsheet-only cases

Until now only cases 357+ (plus a few older ones) had their linked URLs
fetched; the other 252 dossiers held just the text pasted into the
spreadsheet, often only the lede. This pass fetches every linked URL for
those cases so the full text is on file before link rot takes it.

- stage_all.py: new --include-sheet-cases flag that lifts the skip on
  cases holding spreadsheet articles. Resumable as before.
- staging/: raw extracts and index.json for the 252 cases.
- sourced-articles.json, case-files-manifest.json: 188 new UNTRIMMED
  blocks. 179 cases gained at least one fetched article; 73 got none
  (49 BLOCKED, 18 THIN, 9 DEAD, 4 video/social, 3 ERROR).
- sources/*.txt: rebuilt with build_cases.py --all. Sheet pastes are
  kept; fetched blocks sit beside them under the NOT YET TRIMMED banner.
  Files previously committed with CRLF are now LF.
- wayback-availability.json: Wayback snapshots exist for 73 of the 98
  failed URL slots; input for an archive-fetch pass.
- README-START-HERE.md: progress note and next step.

verify_all.py PASSES (1836 checks).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GZZENdTLzNGsbNy4DyF1yt

merge-output/staging/249/01_newswire-lk.txt

@@ -0,0 +1,19 @@
+Chinese group kidnap & rob fellow businessman in Colombo - Newswire
+
+Chinese group kidnap & rob fellow businessman in Colombo
+
+A group of Chinese nationals residing in Sri Lanka have allegedly abducted a fellow Chinese businessman and robbed him of approximately USD 60,000.
+
+According to the Police, the victim, who operates a store on R.A. De Mel Mawatha in Colpetty, was abducted around 9:00 pm last Friday (22).
+
+He was reportedly taken away in a vehicle and held captive in a building for about a day.
+
+During his confinement, the suspects allegedly carried out the robbery by transferring the money online.
+
+The Police said the suspects had later abandoned him on a roadside on Saturday afternoon (23).
+
+The victim is reported to have received treatment at a private hospital in Narahenpita for injuries sustained during the abduction.
+
+The Police said he had filed an official complaint with the Colpetty Police last evening. Investigations are underway into the incident. (Newswire)
+
+© 2026 Wire Digital. All Rights Reserved.

merge-output/staging/249/index.json

@@ -0,0 +1,16 @@
+[
+  {
+    "case": 249,
+    "n": 1,
+    "field": "url",
+    "url": "https://www.newswire.lk/2025/08/25/chinese-group-kidnap-rob-fellow-businessman-in-colombo/",
+    "host": "newswire.lk",
+    "fetched_at": "2026-09-05T12:46:34+00:00",
+    "verdict": "FETCHED",
+    "method": "raw",
+    "http": 200,
+    "chars": 1033,
+    "sha256": "9a96d17fdd37ebd1aa8139d91a52378b9473a2b55528ec0232ebcd5548ca6d98",
+    "final_url": null
+  }
+]