Sprint 286: OperationTaxonomy + LibraryCapabilityLedger (steps 1958-1962)

Phase 6 Library Dispatch foundation. Five new headers:
- OperationDomain: dot-key hierarchy with parent traversal
- LibraryCapabilityRecord: score/APIs/weaknesses + validator
- LibraryCapabilityLedger: (library, domain) -> record registry
- OperationTaxonomy: 40+ domain tree, keyword-based classify()
- Sprint286IntegrationSummary: 8-library seed ledger + verified lookups

25/25 tests passing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

editor/src/LibraryCapabilityRecord.h

@@ -0,0 +1,43 @@
+#pragma once
+// Step 1959: LibraryCapabilityRecord
+// Struct representing a library's capability for one operation domain.
+// Score 0.0 = not applicable, 1.0 = reference implementation.
+
+#include <string>
+#include <vector>
+
+namespace whetstone {
+
+struct LibraryCapabilityRecord {
+    std::string libraryId;       // e.g. "nlohmann_json"
+    std::string operationDomain; // e.g. "serialization.json"
+    float       score       = 0.0f; // [0.0, 1.0]
+    std::vector<std::string> preferredAPIs;
+    std::vector<std::string> knownWeaknesses;
+    bool        notApplicable = false;
+    std::string annotatedAt;     // ISO date string, e.g. "2026-03-02"
+    std::string source;          // annotation source description
+};
+
+class LibraryCapabilityRecordValidator {
+public:
+    struct ValidationResult {
+        bool        valid = true;
+        std::string error;
+    };
+
+    ValidationResult validate(const LibraryCapabilityRecord& r) const {
+        if (r.libraryId.empty())
+            return {false, "libraryId must not be empty"};
+        if (r.operationDomain.empty())
+            return {false, "operationDomain must not be empty"};
+        if (r.score < 0.0f || r.score > 1.0f)
+            return {false, "score must be in [0.0, 1.0], got " +
+                               std::to_string(r.score)};
+        if (r.notApplicable && r.score > 0.0f)
+            return {false, "notApplicable=true is inconsistent with score > 0.0"};
+        return {true, ""};
+    }
+};
+
+} // namespace whetstone