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/access_denied.rhai

@@ -0,0 +1,8 @@
+print("Attempting to access context with non-signatories...");
+print("Participants: [dave, eve]");
+print("Signatories: [alice, bob, charlie]");
+
+// This should fail because neither dave nor eve are signatories
+let ctx = get_context(["dave", "eve"]);
+
+"This should not succeed!"