fix(git-master): inject watermark only when enabled instead of overriding defaults

The watermark (commit footer and co-author) was inconsistently applied because:
1. The skill tool didn't receive gitMasterConfig
2. The approach was 'default ON, inject DISABLED override' which LLMs sometimes ignored

This refactors to 'inject only when enabled' approach:
- Remove hardcoded watermark section from base templates
- Dynamically inject section 5.5 based on config values
- Default is still ON (both true when no config)
- When both disabled, no injection occurs (clean prompt)

Also fixes missing config propagation to skill tool and createBuiltinAgents.

src/index.ts

@@ -281,6 +281,7 @@ const OhMyOpenCodePlugin: Plugin = async (ctx) => {
     skills: mergedSkills,
     mcpManager: skillMcpManager,
     getSessionID: getSessionIDForMcp,
+    gitMasterConfig: pluginConfig.git_master,
   });
   const skillMcpTool = createSkillMcpTool({
     manager: skillMcpManager,