feat: add first-run welcome message with SessionStart hook

- Added FIRST_RUN marker file to detect fresh installs
- Configured SessionStart hook to show welcome message
- Styled message with markdown formatting
- init-bootstrap removes marker after setup completion
- No external shell scripts needed - inline command in settings.json

.claude/settings.json

@@ -0,0 +1,15 @@
+{
+  "hooks": {
+    "SessionStart": [
+      {
+        "matcher": "startup",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "[ -f FIRST_RUN ] && echo '{\"hookSpecificOutput\":{\"hookEventName\":\"SessionStart\",\"additionalContext\":\"# 🚀 Welcome to Claudesidian!\\n\\n**This appears to be your first time using this vault.**\\n\\n## Quick Start\\n\\nRun the setup wizard:\\n\\n```\\n/init-bootstrap\\n```\\n\\n## What this will do:\\n\\n✅ Set up your personalized configuration\\n✅ Disconnect from the original repository  \\n✅ Help you import any existing Obsidian vault\\n✅ Configure your preferred workflow\\n✅ Create your PARA folder structure\\n\\nThe setup wizard will guide you through everything!\"}}' || true"
+          }
+        ]
+      }
+    ]
+  }
+}