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/note.rhai

@@ -0,0 +1,20 @@
+print("Creating context for [alice, bob]...");
+let ctx = get_context(["alice", "bob"]);
+print("✓ Context ID: " + ctx.context_id());
+
+print("\nCreating note...");
+let note = note("notes")
+    .title("Sprint Planning Meeting")
+    .content("Discussed Q1 2025 roadmap and milestones")
+    .tag("sprint", "2025-Q1")
+    .tag("team", "engineering")
+    .tag("priority", "high")
+    .mime("text/markdown");
+
+print("✓ Note created");
+
+print("\nStoring note in context...");
+ctx.save(note);
+print("✓ Note stored");
+
+"Note 'Sprint Planning Meeting' created and stored successfully"