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/features/opencode-skill-loader/skill-content.test.ts

@@ -160,8 +160,8 @@ describe("resolveMultipleSkillsAsync", () => {
 		expect(result.resolved.get("playwright")).toContain("Playwright Browser Automation")
 	})
 
-	it("should support git-master config injection", async () => {
-		// #given: git-master skill with config override
+	it("should NOT inject watermark when both options are disabled", async () => {
+		// #given: git-master skill with watermark disabled
 		const skillNames = ["git-master"]
 		const options = {
 			gitMasterConfig: {
@@ -173,12 +173,84 @@ describe("resolveMultipleSkillsAsync", () => {
 		// #when: resolving with git-master config
 		const result = await resolveMultipleSkillsAsync(skillNames, options)
 
-		// #then: config values injected into template
+		// #then: no watermark section injected
 		expect(result.resolved.size).toBe(1)
 		expect(result.notFound).toEqual([])
 		const gitMasterContent = result.resolved.get("git-master")
-		expect(gitMasterContent).toContain("commit_footer")
-		expect(gitMasterContent).toContain("DISABLED")
+		expect(gitMasterContent).not.toContain("Ultraworked with")
+		expect(gitMasterContent).not.toContain("Co-authored-by: Sisyphus")
+	})
+
+	it("should inject watermark when enabled (default)", async () => {
+		// #given: git-master skill with default config (watermark enabled)
+		const skillNames = ["git-master"]
+		const options = {
+			gitMasterConfig: {
+				commit_footer: true,
+				include_co_authored_by: true,
+			},
+		}
+
+		// #when: resolving with git-master config
+		const result = await resolveMultipleSkillsAsync(skillNames, options)
+
+		// #then: watermark section is injected
+		expect(result.resolved.size).toBe(1)
+		const gitMasterContent = result.resolved.get("git-master")
+		expect(gitMasterContent).toContain("Ultraworked with [Sisyphus]")
+		expect(gitMasterContent).toContain("Co-authored-by: Sisyphus")
+	})
+
+	it("should inject only footer when co-author is disabled", async () => {
+		// #given: git-master skill with only footer enabled
+		const skillNames = ["git-master"]
+		const options = {
+			gitMasterConfig: {
+				commit_footer: true,
+				include_co_authored_by: false,
+			},
+		}
+
+		// #when: resolving with git-master config
+		const result = await resolveMultipleSkillsAsync(skillNames, options)
+
+		// #then: only footer is injected
+		const gitMasterContent = result.resolved.get("git-master")
+		expect(gitMasterContent).toContain("Ultraworked with [Sisyphus]")
+		expect(gitMasterContent).not.toContain("Co-authored-by: Sisyphus")
+	})
+
+	it("should inject watermark by default when no config provided", async () => {
+		// #given: git-master skill with NO config (default behavior)
+		const skillNames = ["git-master"]
+
+		// #when: resolving without any gitMasterConfig
+		const result = await resolveMultipleSkillsAsync(skillNames)
+
+		// #then: watermark is injected (default is ON)
+		expect(result.resolved.size).toBe(1)
+		const gitMasterContent = result.resolved.get("git-master")
+		expect(gitMasterContent).toContain("Ultraworked with [Sisyphus]")
+		expect(gitMasterContent).toContain("Co-authored-by: Sisyphus")
+	})
+
+	it("should inject only co-author when footer is disabled", async () => {
+		// #given: git-master skill with only co-author enabled
+		const skillNames = ["git-master"]
+		const options = {
+			gitMasterConfig: {
+				commit_footer: false,
+				include_co_authored_by: true,
+			},
+		}
+
+		// #when: resolving with git-master config
+		const result = await resolveMultipleSkillsAsync(skillNames, options)
+
+		// #then: only co-author is injected
+		const gitMasterContent = result.resolved.get("git-master")
+		expect(gitMasterContent).not.toContain("Ultraworked with [Sisyphus]")
+		expect(gitMasterContent).toContain("Co-authored-by: Sisyphus")
 	})
 
 	it("should handle empty array", async () => {