feat(timeline): implement TimelineService for building and formatting timeline items

- Extracted timeline-related functionality from mcp-server.ts to a dedicated TimelineService class.
- Added methods to build, filter, and format timeline items based on observations, sessions, and prompts.
- Introduced interfaces for TimelineItem and TimelineData to standardize data structures.
- Implemented sorting and grouping of timeline items by date, with markdown formatting for output.
- Included utility methods for date and time formatting, as well as token estimation.

plugin/.mcp.json

@@ -2,7 +2,7 @@
   "mcpServers": {
     "claude-mem-search": {
       "type": "stdio",
-      "command": "${CLAUDE_PLUGIN_ROOT}/scripts/search-server.cjs"
+      "command": "${CLAUDE_PLUGIN_ROOT}/scripts/mcp-server.cjs"
     }
   }
 }