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

schemas/document.schema.json

@@ -47,8 +47,15 @@
         "same_as": {
           "type": "array",
           "items": {
-            "type": "string",
-            "pattern": "^(doi|arxiv|isbn|pmid|pmcid|openalex|url|lode):[^ ]+$"
+            "anyOf": [
+              {
+                "type": "string",
+                "pattern": "^(doi|arxiv|isbn|pmid|pmcid|openalex|url):[^ ]+$"
+              },
+              {
+                "$ref": "common.schema.json#/$defs/claimRef"
+              }
+            ]
           },
           "uniqueItems": true
         }