cli: maturity polish — color, error translation, tabwriter consistency

Adds three small but high-leverage presentation tweaks for v0.1:

1. internal/cli/style is a new ~70 LOC package with Pass/Fail/Warn/
   Dim/Bold helpers. Each is TTY-gated and obeys NO_COLOR. No
   external dep. Wired into the doctor PASS/FAIL/WARN status, the
   "banger:" error prefix on stderr, and the dim 'ready in <elapsed>'
   line.
2. internal/cli/errors translates rpc.ErrorResponse into user-facing
   text. operation_failed becomes invisible (the message wins);
   not_found, already_exists, bad_request, bad_version, unauthorized,
   unknown_method get short labels; unknown codes pass through. The
   daemon-attached op_id lands in dim parens — paste into
   journalctl --grep to find the daemon log line that produced the
   failure.
3. Tabwriter config converges on (0, 8, 2, ' ', 0) across every
   list/table command. The vm prune confirmation table picked up the
   right config; system install + system status switched from bare
   "key: value\n" lines to tabular form. printVMSpecLine drops its
   Unicode middle dot for an ASCII '|' so terminals without UTF-8
   render cleanly.

Tests cover translateRPCError for every code, style helpers no-op
on non-TTY and under NO_COLOR. Smoke status greps switch from
"key: value" to "key   value" to match the new format.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/cli/vm_create.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"banger/internal/api"
+	"banger/internal/cli/style"
 	"banger/internal/config"
 	"banger/internal/model"
 	"banger/internal/paths"
@@ -52,7 +53,7 @@ func printVMSpecLine(out io.Writer, params api.VMCreateParams) {
 			diskBytes = parsed
 		}
 	}
-	_, _ = fmt.Fprintf(out, "spec: %d vcpu · %d MiB · %s disk\n",
+	_, _ = fmt.Fprintf(out, "spec: %d vcpu | %d MiB | %s disk\n",
 		vcpu, memory, model.FormatSizeBytes(diskBytes))
 }
 
@@ -75,7 +76,8 @@ func (d *deps) runVMCreate(ctx context.Context, socketPath string, stderr io.Wri
 		if op.Done {
 			renderer.render(op)
 			if op.Success && op.VM != nil {
-				_, _ = fmt.Fprintf(stderr, "[vm create] ready in %s\n", formatVMCreateElapsed(time.Since(start)))
+				elapsed := formatVMCreateElapsed(time.Since(start))
+				_, _ = fmt.Fprintf(stderr, "[vm create] ready in %s\n", style.Dim(stderr, elapsed))
 				return *op.VM, nil
 			}
 			if strings.TrimSpace(op.Error) == "" {