fix: anchored input patterns end at the last character (/D)

Without /D, "$" also matches before a trailing "\n", so "custom_meta_telefon\n",
a color setting "5\n" (stored as sent) or a whole reference followed by "\n"
passed VariableRef. Added /D to every ^...$ pattern that validates client or
admin input:
- VariableRef META_KEY, NUMBER, WHOLE (canonical/typeOf; Placeholders::field
  shares META_KEY)
- Cursor::decode, GuideRepository topic names (MCP input and filter keys)
- ExposurePolicy::sanitize ability keys and group ids, LogTab list filters

Not changed: Placeholders::PATTERN (runs on trim()), Warnings hex checks (hints
only), NodeSummary/AttrPathIndex/LogListTable (stored or Divi data, no client
input). Each fixed pattern has a test with a trailing "\n" that is rejected.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7

tests/Unit/Guides/GuideRepositoryTest.php

@@ -76,6 +76,15 @@ final class GuideRepositoryTest extends TestCase
         self::assertNull($this->guides->get('not-string'));
     }
 
+    /** "$" without /D also matches before a trailing newline – such a filter topic is no topic name. */
+    public function testATopicWithTrailingNewlineIsRejected(): void
+    {
+        Filters\expectApplied('lit_mcp_guides')->andReturn(["site-rules\n" => 'eingeschleust']);
+
+        self::assertSame(['divi-shortform', 'overview'], $this->guides->topics());
+        self::assertNull($this->guides->get("site-rules\n"));
+    }
+
     public function testANonArrayFilterResultIsIgnored(): void
     {
         Filters\expectApplied('lit_mcp_guides')->andReturn('kaputt');