feat: scienting-math/1 sources and derived/math.jsonl; lode references; stress fixes

Math content may say its source is in scienting-math/1's canonical TeX (form,
in no hash); derived/math.jsonl holds papermath's tree, symbols and issues,
and the validator now checks derived files. A symbol annotation names its
symbol by key; lode claim references use lode's tag and pin syntax. The zip
reader refuses entries zipfile cannot read, and checkpoint lines end in LF only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017R7sgDNvUGWY2zFPCq2JH6

context/scienting-1.jsonld

@@ -21,6 +21,7 @@
     "pin": "sct:pin",
     "role": "sct:role",
     "symbol": "sct:symbol",
+    "key": "sct:symbolKey",
     "verdict": "sct:verdict",
     "reason": "sct:reason",
     "reference": "sct:reference",