Optimize webhooks JSON with compact format and string interning

- Convert params to compact array format (type-based dispatch)
- Intern duplicate property names into string table
- Use negative indices for object references to distinguish from string indices
- Rename objects.json → webhooks.objects.json, add webhooks.strings.json
- Move event filters to JSON for maintainability
- Add CI validation job to verify optimization correctness

Reduces combined minified size by ~67% (453 KB → 148 KB), ~27% gzipped (23 KB → 17 KB).

.gitignore

@@ -7,7 +7,8 @@ node_modules
 # Minified JSON (generated at build time)
 *.min.json
 
-# Intermediate JSON for size comparison (generated by update-webhooks --all)
-*.all.json
-*.drop.json
-*.strip.json
+# Full webhooks source (generated by update-webhooks, used for validation tests)
+*.full.json
+
+# Validation marker (generated by tests)
+*.validation-complete