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/051/01_northamptonchron-co-uk.txt

@@ -0,0 +1,19 @@
+Masked men with weapons rob Northampton shop for bitcoin machine
+
+Robbers in Northampton threatened a shopkeeper with a machete for a device that turns cash into digital currency.
+
+At around 8.30pm on Tuesday (March 12) three men went to the Costcutter shop on St Leonard’s Road, in Far Cotton, leaving one person waiting outside, Northamptonshire Police today confirmed.
+
+Two men then went inside, one threatened staff with a curved machete while the other smashed a Bitcoin machine off the shop wall with a sledgehammer.
+
+The offenders then left the shop with the machine, walking away along Haines Road and Euston Road.
+
+A spokeswoman for Northamptonshire Police said: "All the men wore face coverings and gloves. The one with the machete is described as wearing a black balaclava, black puffer parka jacket, blue jogging bottoms and light coloured trainers.
+
+"The man with the sledgehammer wore a black balaclava, grey/green puffer style parka jacket, black jogging bottoms and black trainers.
+
+"The third man wore a grey puffer style parka jacket and had a grey face covering."
+
+Anyone who witnessed the robbery, saw the men in the area at the time, or who has information about the incident is asked to call Northamptonshire Police on 101.
+
+© 2026 Iconic Media Group Ltd. All rights reserved.Cookie SettingsTerms and ConditionsPrivacy notice

merge-output/staging/051/index.json

@@ -0,0 +1,16 @@
+[
+  {
+    "case": 51,
+    "n": 1,
+    "field": "url",
+    "url": "https://www.northamptonchron.co.uk/news/masked-men-with-weapons-rob-northampton-shop-for-bitcoin-machine-73035",
+    "host": "northamptonchron.co.uk",
+    "fetched_at": "2026-09-05T12:54:58+00:00",
+    "verdict": "FETCHED",
+    "method": "raw",
+    "http": 200,
+    "chars": 1347,
+    "sha256": "7aebab7b9e2f653214cd7ae384adb4842d0802a247562c3384bf51a57c25d62e",
+    "final_url": null
+  }
+]