feat: add ErrorContextAnalyser for sliding-window error/warning surfacing

Walks Entry[] once and emits one ErrorContextProblem per ERROR or
WARNING entry, attaching up to 20 entries before and 20 after as
context. Overlapping windows clip the second hit's before- and
after-ranges so no Entry appears in two context arrays. Caps emission
at 500 hits and adds an ErrorContextTruncatedInformation when reached.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Analysis/ProjectZomboid/ErrorContextTruncatedInformation.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace IndifferentKetchup\Codex\Analysis\ProjectZomboid;
+
+use IndifferentKetchup\Codex\Analysis\Information;
+use IndifferentKetchup\Codex\Analysis\InsightInterface;
+
+/**
+ * Emitted by ErrorContextAnalyser exactly once when its hit cap is
+ * reached, so downstream consumers can surface a "results truncated"
+ * notice instead of silently dropping subsequent error/warning hits.
+ */
+class ErrorContextTruncatedInformation extends Information
+{
+    private int $hitCap = 0;
+
+    /**
+     * @param int $hitCap the cap that was hit (mirrors
+     *     ErrorContextAnalyser::HIT_CAP at emission time)
+     * @return $this
+     */
+    public function setHitCap(int $hitCap): static
+    {
+        $this->hitCap = $hitCap;
+        $this->setLabel('Error context');
+        $this->setValue(sprintf('truncated after %d hits', $hitCap));
+        return $this;
+    }
+
+    /**
+     * @return int
+     */
+    public function getHitCap(): int
+    {
+        return $this->hitCap;
+    }
+
+    public function isEqual(InsightInterface $insight): bool
+    {
+        return $insight instanceof self;
+    }
+}