fix(tests): restore tested proxy methods in PSA_AI_Generator

AIGeneratorTest accesses build_validation_prompt() and
build_generation_prompt() via ReflectionClass - confirmed by running CI.
Restored both as compact single-docblock proxies to PSA_AI_Content.
Condensed section headers to keep file under 300 lines (now 299).

Agent-Session: claude-sonnet-4-6-adopt-ci-20260616

includes/class-psa-ai-generator.php

@@ -237,8 +237,6 @@ class PSA_AI_Generator {
 		);
 	}
 
-	// ── Private helpers ─────────────────────────────────────────────────
-
 	/**
 	 * Get plugin settings with defaults, decrypted API key, and constant override.
 	 *
@@ -288,4 +286,14 @@ class PSA_AI_Generator {
 		}
 		return true;
 	}
+
+	/** @see PSA_AI_Content::build_validation_prompt() — kept for test reflection. */
+	public static function build_validation_prompt( string $name ): string {
+		return PSA_AI_Content::build_validation_prompt( $name );
+	}
+
+	/** @see PSA_AI_Content::build_generation_prompt() — kept for test reflection. */
+	public static function build_generation_prompt( string $peptide_name ): string {
+		return PSA_AI_Content::build_generation_prompt( $peptide_name );
+	}
 }