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/project.schema.json

@@ -131,7 +131,21 @@
                 "type",
                 "ref"
               ],
-              "additionalProperties": false
+              "additionalProperties": false,
+              "if": {
+                "properties": {
+                  "type": {
+                    "const": "claim"
+                  }
+                }
+              },
+              "then": {
+                "properties": {
+                  "ref": {
+                    "$ref": "common.schema.json#/$defs/claimRef"
+                  }
+                }
+              }
             },
             "minItems": 1
           }