[fern-autoversion] chore: enrich PHPDoc comments across types and request DTOs

Add descriptive class-level and property-level PHPDoc comments to
dozens of types and request DTOs throughout the SDK. These additions
improve IDE autocompletion, hover documentation, and generated API
reference output without changing any public API signatures, method
behavior, or serialization logic.

Key changes:
- Add class-level docblocks to types such as `Assistant`, `Call`, `Edge`, `CompliancePlan`, `BackoffPlan`, and many more
- Expand property-level `@var` comments with human-readable descriptions (e.g., `$firstMessageInterruptionsEnabled`, `$compliancePlan`, `$keypadInputPlan`)
- Consolidate multi-line prose comments into single-line `@var` annotations (e.g., `BackoffPlan::$excludedStatusCodes`, `CustomerSpeechTimeoutOptions::$triggerResetMode`)

🌿 Generated with Fern

Author: fern-api[bot]

.fern/metadata.json

@@ -11,5 +11,5 @@
   "invokedBy": "ci",
   "requestedVersion": "AUTO",
   "ciProvider": "unknown",
-  "sdkVersion": "0.0.0-fern-placeholder"
+  "sdkVersion": "2.0.1"
 }

composer.json

@@ -1,6 +1,6 @@
 {
   "name": "vapi/vapi",
-  "version": "0.0.0-fern-placeholder",
+  "version": "2.0.1",
   "description": "Vapi PHP Library",
   "keywords": [
     "vapi",

src/VapiClient.php

@@ -131,8 +131,8 @@ public function __construct(
             'Authorization' => "Bearer $token",
             'X-Fern-Language' => 'PHP',
             'X-Fern-SDK-Name' => 'Vapi',
-            'X-Fern-SDK-Version' => '0.0.0-fern-placeholder',
-            'User-Agent' => 'vapi/vapi/0.0.0-fern-placeholder',
+            'X-Fern-SDK-Version' => '2.0.1',
+            'User-Agent' => 'vapi/vapi/2.0.1',
         ];
 
         $this->options = $options ?? [];