feat(ai): implement AI memory system with context extraction and storage

Add comprehensive AI memory functionality including:
- Memory context preparation and caching
- Fact extraction from conversations
- Memory search and retrieval with category support
- JSON-based memory update operations (add/update/delete)
- Memory deduplication and normalization
- Integration with AI conversation flow

The system extracts relevant facts from conversations, stores them with
categories, and provides contextual memory to enhance AI responses.

Source/WulaFallenEmpire/EventSystem/AI/MemoryPrompts.cs

@@ -0,0 +1,45 @@
+using System.Globalization;
+
+namespace WulaFallenEmpire.EventSystem.AI
+{
+    public static class MemoryPrompts
+    {
+        public const string FactExtractionPrompt =
+@"You are extracting long-term memory about the player from the conversation below.
+Return JSON only, no extra text.
+Schema:
+{{""facts"":[{{""text"":""..."",""category"":""preference|personal|plan|colony|misc""}}]}}
+Rules:
+- Keep only stable, reusable facts about the player or colony.
+- Ignore transient tool results, numbers, or one-off actions.
+- Do not invent facts.
+Conversation:
+{0}";
+
+        public const string MemoryUpdatePrompt =
+@"You are updating a memory store.
+Given existing memories and new facts, decide ADD, UPDATE, DELETE, or NONE.
+Return JSON only, no extra text.
+Schema:
+{{""memory"":[{{""id"":""..."",""text"":""..."",""category"":""preference|personal|plan|colony|misc"",""event"":""ADD|UPDATE|DELETE|NONE""}}]}}
+Rules:
+- UPDATE if a new fact refines or corrects an existing memory.
+- DELETE if a memory is contradicted by new facts.
+- ADD for genuinely new information.
+- NONE if no change is needed.
+Existing memories (JSON):
+{0}
+New facts (JSON):
+{1}";
+
+        public static string BuildFactExtractionPrompt(string conversation)
+        {
+            return string.Format(CultureInfo.InvariantCulture, FactExtractionPrompt, conversation ?? "");
+        }
+
+        public static string BuildMemoryUpdatePrompt(string existingMemoriesJson, string newFactsJson)
+        {
+            return string.Format(CultureInfo.InvariantCulture, MemoryUpdatePrompt, existingMemoriesJson ?? "[]", newFactsJson ?? "[]");
+        }
+    }
+}