Fix PHP symbol retrieval: declare missing Intelephense client capabilities (#1099)

Fix PHP symbol retrieval via Intelephense LSP

* intelephense.py: Add missing client capability declarations for
  documentSymbol (with hierarchical support), references, hover, and
  workspace symbol. Without these, Intelephense does not advertise
  documentSymbolProvider and returns empty results for get_symbols_overview.

Add PHP tests validating hierarchical symbols and LS routing fix

- test_document_symbols_hierarchical_structure: verifies Intelephense
  returns DocumentSymbol[] with class/method hierarchy (not flat
  SymbolInformation[]) when hierarchicalDocumentSymbolSupport is declared

- test_full_symbol_tree_within_file: verifies request_full_symbol_tree
  scoped to sample.php returns Dog/Animal/greet/fetch with Dog containing
  greet as a child (not at root level)

- test_find_symbol_within_php_file: verifies find_symbol with a PHP
  file path (relative_path=) routes to the PHP language server via
  get_language_server() rather than iterating all servers

Peripheral changes:

- symbol.py (LanguageServerSymbolRetriever.find_symbols): When searching
  within a specific file, route to the file-type-appropriate language server
  via get_language_server() instead of querying all servers. This ensures
  PHP files are served by Intelephense and not silently skipped.

test/resources/repos/php/test_repo/sample.php

@@ -0,0 +1,122 @@
+<?php
+
+namespace SerenaTest;
+
+/**
+ * Interface for objects that can greet.
+ */
+interface GreeterInterface
+{
+    public function greet(string $name): string;
+}
+
+/**
+ * Abstract base class for animals.
+ */
+abstract class Animal
+{
+    protected string $name;
+    protected int $age;
+
+    public function __construct(string $name, int $age)
+    {
+        $this->name = $name;
+        $this->age  = $age;
+    }
+
+    public function getName(): string
+    {
+        return $this->name;
+    }
+
+    public function getAge(): int
+    {
+        return $this->age;
+    }
+
+    abstract public function describe(): string;
+}
+
+/**
+ * A concrete animal that can greet visitors.
+ */
+class Dog extends Animal implements GreeterInterface
+{
+    private string $breed;
+
+    public function __construct(string $name, int $age, string $breed)
+    {
+        parent::__construct($name, $age);
+        $this->breed = $breed;
+    }
+
+    public function greet(string $visitorName): string
+    {
+        return "Woof! I'm {$this->name}. Hello, {$visitorName}!";
+    }
+
+    public function getBreed(): string
+    {
+        return $this->breed;
+    }
+
+    public function describe(): string
+    {
+        return "Dog: {$this->name} ({$this->breed}), age {$this->age}";
+    }
+
+    public function fetch(string $item): string
+    {
+        return "{$this->name} fetches the {$item}!";
+    }
+}
+
+/**
+ * Another concrete animal.
+ */
+class Cat extends Animal
+{
+    private bool $indoor;
+
+    public function __construct(string $name, int $age, bool $indoor = true)
+    {
+        parent::__construct($name, $age);
+        $this->indoor = $indoor;
+    }
+
+    public function isIndoor(): bool
+    {
+        return $this->indoor;
+    }
+
+    public function describe(): string
+    {
+        $type = $this->indoor ? 'indoor' : 'outdoor';
+        return "Cat: {$this->name} ({$type}), age {$this->age}";
+    }
+}
+
+const MAX_ANIMALS = 100;
+const DEFAULT_BREED = 'Mixed';
+
+/**
+ * Factory function to create an animal by type name.
+ */
+function createAnimal(string $type, string $name, int $age): Animal
+{
+    return match ($type) {
+        'dog' => new Dog($name, $age, DEFAULT_BREED),
+        'cat' => new Cat($name, $age),
+        default => throw new \InvalidArgumentException("Unknown animal type: {$type}"),
+    };
+}
+
+/**
+ * Returns a summary string for a list of animals.
+ *
+ * @param Animal[] $animals
+ */
+function summarizeAnimals(array $animals): string
+{
+    return implode(', ', array_map(fn(Animal $a) => $a->describe(), $animals));
+}