Bootstrap vm run tooling before attach

Speed up first use of repo backed VMs by bootstrapping obvious tools before
the best effort LLM harness runs.

Add a host side tooling plan for pinned Go, Node, Python, and Rust versions,
summarize that plan in the uploaded prompt, and run repo mise install plus
guest global mise use -g --pin steps before the bounded opencode inspection.

Keep the harness non fatal, prefer host opencode attach when the client
supports it, fall back to guest opencode over SSH for older clients, and
cover the new flow with CLI plus planner tests.

Validation:
- go test ./internal/cli ./internal/toolingplan
- GOCACHE=/tmp/banger-gocache go test ./...
- make build

internal/toolingplan/plan.go

@@ -0,0 +1,94 @@
+package toolingplan
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"sort"
+)
+
+type InstallStep struct {
+	Tool    string
+	Version string
+	Source  string
+	Reason  string
+}
+
+type SkipNote struct {
+	Target string
+	Reason string
+}
+
+type Plan struct {
+	RepoManagedTools []string
+	Steps            []InstallStep
+	Skips            []SkipNote
+}
+
+type detector interface {
+	detect(context.Context, string, map[string]struct{}) detectionResult
+}
+
+type detectionResult struct {
+	Steps []InstallStep
+	Skips []SkipNote
+}
+
+var detectors = []detector{
+	goDetector{},
+	nodeDetector{},
+	pythonDetector{},
+	rustDetector{},
+}
+
+func Build(ctx context.Context, repoRoot string) Plan {
+	managedTools, managedSkips := repoManagedTools(repoRoot)
+	steps := make([]InstallStep, 0)
+	skips := append([]SkipNote(nil), managedSkips...)
+	for _, detector := range detectors {
+		result := detector.detect(ctx, repoRoot, managedTools)
+		steps = append(steps, result.Steps...)
+		skips = append(skips, result.Skips...)
+	}
+	sort.Slice(steps, func(i, j int) bool {
+		if steps[i].Tool != steps[j].Tool {
+			return steps[i].Tool < steps[j].Tool
+		}
+		if steps[i].Version != steps[j].Version {
+			return steps[i].Version < steps[j].Version
+		}
+		return steps[i].Source < steps[j].Source
+	})
+	sort.Slice(skips, func(i, j int) bool {
+		if skips[i].Target != skips[j].Target {
+			return skips[i].Target < skips[j].Target
+		}
+		return skips[i].Reason < skips[j].Reason
+	})
+	repoManagedList := make([]string, 0, len(managedTools))
+	for tool := range managedTools {
+		repoManagedList = append(repoManagedList, tool)
+	}
+	sort.Strings(repoManagedList)
+	return Plan{
+		RepoManagedTools: repoManagedList,
+		Steps:            steps,
+		Skips:            skips,
+	}
+}
+
+func readRepoFile(repoRoot, relativePath string) (string, bool, error) {
+	data, err := os.ReadFile(filepath.Join(repoRoot, relativePath))
+	if err != nil {
+		if os.IsNotExist(err) {
+			return "", false, nil
+		}
+		return "", false, err
+	}
+	return string(data), true, nil
+}
+
+func alreadyManaged(tool string, managedTools map[string]struct{}) bool {
+	_, ok := managedTools[tool]
+	return ok
+}