homelab: add tf verbs + stack/git-crypt substrate

Adds the tf verb-group and the resolver substrate beneath it, continuing the
v0.1 infra-loop build.

- substrate: findInfraRoot (walk up to terragrunt.hcl + stacks/), stack→dir
  resolver, and repo/remote/git-crypt detection (preferRemote forgejo>origin,
  hasGitCryptAttr, gitCryptFlags) — the last is for `work` next.
- tf plan/validate/fmt/force-unlock/apply, resolving the stack from cwd and
  delegating to scripts/tg (which owns state decrypt/encrypt, the Vault lock,
  and the ingress auth-comment check) rather than calling terragrunt directly.
- tf apply is presence-coupled: claims stack:<name>, ALWAYS releases on exit
  (normal, error, or SIGINT/SIGTERM via sync.Once + signal handler) — fixing
  the documented ~200-claim leak — and prints an out-of-band reminder since CI
  applies canonically on push.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

cli/stack.go

@@ -0,0 +1,54 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+)
+
+// findInfraRoot walks up from start to the infra repo root — the directory
+// holding both terragrunt.hcl and a stacks/ directory.
+func findInfraRoot(start string) (string, error) {
+	dir := start
+	for {
+		if isFile(filepath.Join(dir, "terragrunt.hcl")) && isDir(filepath.Join(dir, "stacks")) {
+			return dir, nil
+		}
+		parent := filepath.Dir(dir)
+		if parent == dir {
+			return "", fmt.Errorf("not inside an infra checkout (no terragrunt.hcl + stacks/ found above %s)", start)
+		}
+		dir = parent
+	}
+}
+
+// resolveStack maps a bare stack name to its directory under <infraRoot>/stacks.
+func resolveStack(infraRoot, name string) (string, error) {
+	dir := filepath.Join(infraRoot, "stacks", name)
+	if isDir(dir) {
+		return dir, nil
+	}
+	avail := listStacks(infraRoot)
+	return "", fmt.Errorf("stack %q not found under stacks/; available: %s", name, strings.Join(avail, ", "))
+}
+
+// listStacks returns the sorted names of every directory under <infraRoot>/stacks.
+func listStacks(infraRoot string) []string {
+	entries, err := os.ReadDir(filepath.Join(infraRoot, "stacks"))
+	if err != nil {
+		return nil
+	}
+	var out []string
+	for _, e := range entries {
+		if e.IsDir() {
+			out = append(out, e.Name())
+		}
+	}
+	sort.Strings(out)
+	return out
+}
+
+func isFile(p string) bool { fi, err := os.Stat(p); return err == nil && !fi.IsDir() }
+func isDir(p string) bool  { fi, err := os.Stat(p); return err == nil && fi.IsDir() }