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/routes/api.php

@@ -55,5 +55,6 @@ Route::middleware(JwtAuth::class)->group(function () {
     // PTO
     Route::get('/ptos', [PtoController::class, 'index']);
     Route::post('/ptos', [PtoController::class, 'store']);
+    Route::delete('/ptos/{id}', [PtoController::class, 'destroy']);
     Route::put('/ptos/{id}/approve', [PtoController::class, 'approve']);
 });