docs(openspec): add reporting API contract documentation

Add comprehensive API documentation for the reporting endpoint:
- Request/response structure
- View type inference (did/is/will)
- Blank vs explicit zero semantics
- Status values and error responses

Related to enhanced-allocation change.

backend/tests/Unit/AllocationPolicyTest.php

@@ -47,4 +47,13 @@ class AllocationPolicyTest extends TestCase
 
         $this->assertFalse($this->policy->create($developer));
     }
+
+    // 2.3 Unit test: AllocationPolicy allows untracked allocation
+    public function test_manager_can_create_untracked_allocations()
+    {
+        $manager = User::factory()->create(['role' => 'manager']);
+
+        // Policy should allow creating allocations (untracked is just null team_member_id)
+        $this->assertTrue($this->policy->create($manager));
+    }
 }