feat(FN-3869): add github tracking fields and resolver to tasks

Adds GitHub tracking fields to the task model with schema migration, store accessors, and type definitions in `@fusion/core`. New `github-tracking.ts` module exposes a resolver for fetching GitHub issue/PR metadata, integrated into the task store. Test coverage spans the new module, store integratio

Fusion-Task-Id: FN-3869

packages/core/src/db.ts

@@ -88,7 +88,7 @@ export function probeFts5(db: DatabaseSync): boolean {
 
 // ── Schema Definition ────────────────────────────────────────────────
 
-const SCHEMA_VERSION = 70;
+const SCHEMA_VERSION = 71;
 
 function normalizeTaskComments(
   steeringComments: SteeringComment[] | undefined,
@@ -206,6 +206,7 @@ CREATE TABLE IF NOT EXISTS tasks (
   workflowStepResults TEXT DEFAULT '[]',
   prInfo TEXT,
   issueInfo TEXT,
+  githubTracking TEXT,
   sourceIssueProvider TEXT,
   sourceIssueRepository TEXT,
   sourceIssueExternalIssueId TEXT,
@@ -2960,6 +2961,12 @@ export class Database {
       });
     }
 
+    if (version < 71) {
+      this.applyMigration(71, () => {
+        this.addColumnIfMissing("tasks", "githubTracking", "TEXT");
+      });
+    }
+
   }
 
   /**