refactor(gemini-cli): change agent storage from multiple files to single (#308)

* refactor(gemini-cli): change agent storage from multiple files to single concatenated file

- Update configuration to use .gemini/bmad-method/ directory instead of .gemini/agents/
- Implement new logic to concatenate all agent files into single GEMINI.md
- Add backward compatibility for existing settings.json
- Remove old agents directory and update related documentation
- Ensure all agent settings are properly loaded

* fix(ide-setup): change agent trigger symbol from @ to *

The change was made to standardize the agent trigger symbol across the system and avoid confusion with other special characters.

* docs: update gemini cli syntax and file structure

- Change agent mention syntax from @ to * in docs and config
- Update file structure documentation from .gemini/agents/ to .gemini/bmad-method/
- Add gemini cli syntax to workflow guide

* fix(ide-setup): remove redundant contextFileNames handling

tools/installer/config/install.config.yaml

@@ -68,13 +68,14 @@ ide-configurations:
       # 4. Rules are stored in .clinerules/ directory in your project
   gemini:
     name: Gemini CLI
-    rule-dir: .gemini/agents/
-    format: context-files
+    rule-dir: .gemini/bmad-method/
+    format: single-file
+    command-suffix: .md
     instructions: |
       # To use BMad agents with the Gemini CLI:
-      # 1. The installer creates a .gemini/ directory in your project.
-      # 2. It also configures .gemini/settings.json to load all agent files.
-      # 3. Simply mention the agent in your prompt (e.g., "As @dev, ...").
+      # 1. The installer creates a .gemini/bmad-method/ directory in your project.
+      # 2. It concatenates all agent files into a single GEMINI.md file.
+      # 3. Simply mention the agent in your prompt (e.g., "As *dev, ...").
       # 4. The Gemini CLI will automatically have the context for that agent.
   github-copilot:
     name: Github Copilot