fix(installer): use single quotes for description in Gemini workflow templates

Replace triple-quoted """{{description}}""" with single-quoted '{{description}}'
to avoid TOML escaping issues in Gemini workflow templates.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tools/cli/installers/lib/ide/templates/combined/gemini-workflow-yaml.toml

@@ -1,4 +1,4 @@
-description = """{{description}}"""
+description = '{{description}}'
 prompt = """
 Execute the BMAD '{{name}}' workflow.
 

tools/cli/installers/lib/ide/templates/combined/gemini-workflow.toml

@@ -1,4 +1,4 @@
-description = """{{description}}"""
+description = '{{description}}'
 prompt = """
 Execute the BMAD '{{name}}' workflow.