fix(capacity): stabilize PTO flows and calendar consistency

Make PTO creation immediately approved, add PTO deletion, and ensure cache invalidation updates individual/team/revenue capacity consistently.

Harden holiday duplicate handling (422), support PTO-day availability overrides without disabling edits, and align tests plus OpenSpec artifacts with the new behavior.

backend/database/migrations/2024_02_17_000009_create_ptos_table.php

@@ -17,7 +17,7 @@ return new class extends Migration
             $table->date('start_date');
             $table->date('end_date');
             $table->string('reason')->nullable();
-            $table->enum('status', ['pending', 'approved', 'rejected'])->default('pending');
+            $table->enum('status', ['pending', 'approved', 'rejected'])->default('approved');
             $table->timestamps();
         });
     }