Add New Data Modality

---

name: new-modality description: Add a new data modality to the lifelog system (proto, schema, collector module) disable-model-invocation: true

Add a new data modality called: $ARGUMENTS.

Follow this checklist in order:

1. Proto definition: Add message type to proto/lifelog.proto and enum variant to DataModality in proto/lifelog_types.proto
2. Rebuild proto: just check to regenerate code
3. Proto impls: Add DataType + Modality trait impls in common/lifelog-proto/src/lib.rs (follow existing patterns like ScreenFrame)
4. DB schema: Add TableSchema entry in server/src/schema.rs with fields and indexes
5. Collector module: Create collector/src/modules/<name>.rs with the collection logic
6. Register module: Add pub mod <name>; in collector/src/modules/mod.rs and wire into collector startup
7. Validate: Run just validate to ensure everything compiles and tests pass