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>

cmd/banger/main.go

@@ -9,6 +9,7 @@ import (
 	"syscall"
 
 	"banger/internal/cli"
+	"banger/internal/cli/style"
 )
 
 func main() {
@@ -21,7 +22,12 @@ func main() {
 		if errors.As(err, &exitErr) {
 			os.Exit(exitErr.Code)
 		}
-		fmt.Fprintf(os.Stderr, "banger: %v\n", err)
+		// Render the failure through the CLI's translator so RPC
+		// codes become friendly text, op_ids land in parens for
+		// journalctl grepping, and the "banger:" prefix turns red
+		// on a TTY.
+		prefix := style.Fail(os.Stderr, "banger:")
+		fmt.Fprintf(os.Stderr, "%s %s\n", prefix, cli.TranslateError(os.Stderr, err))
 		os.Exit(1)
 	}
 }