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/builtin-skills/git-master/SKILL.md

@@ -529,33 +529,6 @@ IF style == SHORT:
 3. Is it similar to examples from git log?
 
 If ANY check fails -> REWRITE message.
-
-### 5.5 Commit Footer & Co-Author (Configurable)
-
-**Check oh-my-opencode.json for these flags:**
-- `git_master.commit_footer` (default: true) - adds footer message
-- `git_master.include_co_authored_by` (default: true) - adds co-author trailer
-
-If enabled, add Sisyphus attribution to EVERY commit:
-
-1. **Footer in commit body (if `commit_footer: true`):**
-```
-Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)
-```
-
-2. **Co-authored-by trailer (if `include_co_authored_by: true`):**
-```
-Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
-```
-
-**Example (both enabled):**
-```bash
-git commit -m "{Commit Message}" -m "Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)" -m "Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>"
-```
-
-**To disable:** Set in oh-my-opencode.json:
-```json
-{ "git_master": { "commit_footer": false, "include_co_authored_by": false } }
 ```
 </execution>