Add create-plugin command and improve asset management

- Add new create-plugin command to generate plugins from starter template
- Add manifest name subcommand for template context
- Replace hardcoded asset paths with explicit file patterns in embed directive
- Refactor asset build system to use _setup.mk instead of setup.mk
- Update versioning to use pluginctl manifest id for APP_NAME
- Clean up Makefile by removing redundant bundle name definition

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

assets/Makefile

@@ -26,13 +26,6 @@ default: all
 # Verify environment, and define PLUGIN_ID, PLUGIN_VERSION, HAS_SERVER and HAS_WEBAPP as needed.
 include build/setup.mk
 
-BUNDLE_NAME ?= $(PLUGIN_ID)-$(PLUGIN_VERSION).tar.gz
-
-# Include custom makefile, if present
-ifneq ($(wildcard build/custom.mk),)
-	include build/custom.mk
-endif
-
 ifneq ($(MM_DEBUG),)
 	GO_BUILD_GCFLAGS = -gcflags "all=-N -l"
 else
@@ -40,4 +33,4 @@ else
 endif
 
 # Include modular makefiles
-include build/*.mk
+include build/*.mk