feat: reorganize examples and add signature support to JobBuilder

- Reorganized examples into osiris/, sal/, and utils/ folders
- Moved hardcoded scripts to separate .rhai files
- Added signature() method to JobBuilder for job signing
- Updated OSIRIS context to use block_in_place instead of runtime
- Removed runtime field from OsirisContext
- Added typed save() methods for Note and Event objects
- Updated all examples to use new structure and APIs

examples/osiris/event.rhai

@@ -0,0 +1,18 @@
+print("Creating context for [alice, bob]...");
+let ctx = get_context(["alice", "bob"]);
+print("✓ Context ID: " + ctx.context_id());
+
+print("\nCreating event...");
+let event = event("events")
+    .title("Team Retrospective")
+    .description("Review what went well and areas for improvement")
+    .location("Virtual - Zoom Room A")
+    .category("retrospective");
+
+print("✓ Event created");
+
+print("\nStoring event in context...");
+ctx.save(event);
+print("✓ Event stored");
+
+"Event 'Team Retrospective' created and stored successfully"