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/tools/skill/tools.ts

@@ -4,6 +4,7 @@ import { TOOL_DESCRIPTION_NO_SKILLS, TOOL_DESCRIPTION_PREFIX } from "./constants
 import type { SkillArgs, SkillInfo, SkillLoadOptions } from "./types"
 import type { LoadedSkill } from "../../features/opencode-skill-loader"
 import { getAllSkills, extractSkillTemplate } from "../../features/opencode-skill-loader/skill-content"
+import { injectGitMasterConfig } from "../../features/opencode-skill-loader/skill-content"
 import type { SkillMcpManager, SkillMcpClientInfo, SkillMcpServerContext } from "../../features/skill-mcp-manager"
 import type { Tool, Resource, Prompt } from "@modelcontextprotocol/sdk/types.js"
 
@@ -164,7 +165,12 @@ export function createSkillTool(options: SkillLoadOptions = {}): ToolDefinition
         throw new Error(`Skill "${args.name}" not found. Available skills: ${available || "none"}`)
       }
 
-      const body = await extractSkillBody(skill)
+      let body = await extractSkillBody(skill)
+
+      if (args.name === "git-master") {
+        body = injectGitMasterConfig(body, options.gitMasterConfig)
+      }
+
       const dir = skill.path ? dirname(skill.path) : skill.resolvedPath || process.cwd()
 
       const output = [