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/020/01_dailysabah-com.txt

@@ -0,0 +1,21 @@
+Turkish police detain gang who stole bitcoins worth $2.83M | Daily Sabah
+
+Turkish police detain gang who stole bitcoins worth $2.83M
+
+Turkey's cybercrimes police detained a gang of thieves who robbed 450 Bitcoins worth $2.83 million from a businessman in Istanbul's Merter district, reports said Wednesday. The incident marks the first time police carried out an operation to detain criminals involved in stealing cryptocurrencies.
+
+According to reports, the gang, consisting of five people, posed as police and stopped the businessman's car and forced him to give out his passwords of online banking accounts at gunpoint.
+
+The businessman reportedly contacted the police following the incident and filed a criminal complaint and police were able to find the whereabouts of gang members after examination of security cameras around the area.
+
+One of the suspects was reportedly jailed for extortion but had fled, while another suspect proposed to his girlfriend in an extravagant ceremony at a luxurious restaurant in Istanbul.
+
+Police investigation revealed that the suspects had also stolen bitcoin mining devices from three different people in Esenler district.
+
+Keep up to date with what’s happening in Turkey,
+ it’s region and the world.
+
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+
+China's Communist Party marks its centenary

merge-output/staging/020/index.json

@@ -0,0 +1,16 @@
+[
+  {
+    "case": 20,
+    "n": 1,
+    "field": "url",
+    "url": "https://www.dailysabah.com/investigations/2017/11/15/turkish-police-detain-gang-who-stole-bitcoins-worth-283m",
+    "host": "dailysabah.com",
+    "fetched_at": "2026-09-05T12:56:30+00:00",
+    "verdict": "FETCHED",
+    "method": "raw",
+    "http": 200,
+    "chars": 1487,
+    "sha256": "621e7215128ddf5d43f25de13c126f544508dd98260b73be372b3b671087ab5c",
+    "final_url": null
+  }
+]