feature #580 [Agent] Update instructions in SystemPromptInputProcessor (OskarStark)

This PR was squashed before being merged into the main branch.

Discussion
----------

[Agent] Update instructions in `SystemPromptInputProcessor`

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Docs?         | no
| Issues        | --
| License       | MIT

Commits
-------

ffd7bbb [Agent] Update instructions in `SystemPromptInputProcessor`

Author: OskarStark

src/agent/src/InputProcessor/SystemPromptInputProcessor.php

@@ -63,7 +63,9 @@ public function processInput(Input $input): void
             $message = <<<PROMPT
                 {$this->systemPrompt}
 
-                # Available tools
+                # Tools
+
+                The following tools are available to assist you in completing the user's request:
 
                 {$tools}
                 PROMPT;

src/agent/tests/InputProcessor/SystemPromptInputProcessorTest.php

@@ -140,7 +140,9 @@ public function execute(ToolCall $toolCall): mixed
         $this->assertSame(<<<PROMPT
             This is a system prompt
 
-            # Available tools
+            # Tools
+
+            The following tools are available to assist you in completing the user's request:
 
             ## tool_no_params
             A tool without parameters
@@ -180,7 +182,9 @@ public function execute(ToolCall $toolCall): mixed
         $this->assertSame(<<<PROMPT
             My dynamic system prompt.
 
-            # Available tools
+            # Tools
+
+            The following tools are available to assist you in completing the user's request:
 
             ## tool_no_params
             A tool without parameters