feat(debug): add debug MCP skill with hypothesis generation

Implements the debug skill following the same pattern as review. The skill
accepts project_root + error (+ optional context/model/session_id), prepends
session history, and calls the executor to produce 3-5 ordered hypotheses —
diagnosis only, no fixes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/supervisor/main.go

@@ -13,6 +13,7 @@ import (
 	"github.com/mathiasbq/supervisor/internal/skills/brain"
 	"github.com/mathiasbq/supervisor/internal/skills/org"
 	"github.com/mathiasbq/supervisor/internal/skills/retrospective"
+	skilldebug "github.com/mathiasbq/supervisor/internal/skills/debug"
 	"github.com/mathiasbq/supervisor/internal/skills/review"
 	"github.com/mathiasbq/supervisor/internal/skills/sessionlog"
 	"github.com/mathiasbq/supervisor/internal/skills/tdd"
@@ -58,6 +59,12 @@ func main() {
 		os.Exit(1)
 	}
 
+	debugPrompt, err := os.ReadFile(cfg.ConfigDir + "/debug.md")
+	if err != nil {
+		logger.Error("read debug.md", "path", cfg.ConfigDir+"/debug.md", "err", err)
+		os.Exit(1)
+	}
+
 	executor := iexec.New(iexec.Config{
 		SystemPrompt:   string(systemPrompt),
 		LiteLLMBaseURL: cfg.LiteLLMBaseURL,
@@ -97,6 +104,12 @@ func main() {
 		ExecutorFn:   executor.Run,
 		SessionsDir:  cfg.SessionsDir,
 	}))
+	reg.Register(skilldebug.New(skilldebug.Config{
+		SkillPrompt:  string(debugPrompt),
+		DefaultModel: models.Resolve("debug", ""),
+		ExecutorFn:   executor.Run,
+		SessionsDir:  cfg.SessionsDir,
+	}))
 
 	srv := mcp.NewServer(reg)
 	mux := http.NewServeMux()