chore: add changeset for incremental indexing

Author: prosdev

.changeset/incremental-indexing.md

@@ -0,0 +1,19 @@
+---
+"@lytics/dev-agent-core": patch
+"@lytics/dev-agent": patch
+---
+
+Incremental indexing now works! `dev update` detects changed, new, and deleted files.
+
+**What's new:**
+- Only re-indexes files that actually changed (via content hash)
+- Detects new files added since last index
+- Cleans up documents for deleted files
+- Removes orphaned symbols when code is modified
+
+**Usage:**
+```bash
+dev index .     # First run: full index
+dev update      # Fast incremental update
+dev index . --force  # Force full re-index
+```