feat: upgrade Claude Agent SDK from 0.1.9 to 0.1.55 for Skills support

**Critical Fix: Enable Skills in Discord Bot**

The bot was running SDK v0.1.9 which predates Skills support
(released in Oct 2025). This prevented auto-loading of project
Skills like content-router when users posted URLs.

**Changes:**
- Upgrade @anthropic-ai/claude-agent-sdk: ^0.1.9 → ^0.1.55
- Code already prepared with settingSources: ['user', 'project', 'local']
- Code already using new systemPrompt format: { type: 'preset', preset: 'claude_code' }

**Why This Fixes Skills:**
- SDK 0.1.55 includes settingSources option (missing in 0.1.9)
- Skills are loaded from .claude/skills/ via settingSources config
- Auto-detection works when Skills match task relevance

**New Dependencies:**
- zod (peer dep) - Schema validation for SDK
- @img/sharp-linuxmusl-* - Image processing for Alpine Linux containers

**Testing:**
- Skills directory exists: /srv/claude-jobs/obsidian-vault/.claude/skills/
- Code has settingSources configured in all 3 query() calls
- Ready for CI deployment to Hetzner

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: jonathanglasmeyer

discord-server/package-lock.json

@@ -14,7 +14,7 @@
     "cleanup:local": "curl -X POST -s http://localhost:3001/admin/cleanup-threads | jq"
   },
   "dependencies": {
-    "@anthropic-ai/claude-agent-sdk": "^0.1.9",
+    "@anthropic-ai/claude-agent-sdk": "^0.1.55",
     "discord.js": "^14.15.3",
     "dotenv": "^16.3.1",
     "express": "^5.1.0",