feat: triple-toggle CPU display mode via 1 key; add tooltip, font, hit-test

CPU display now cycles through three states with each press of 1:
  0 = CPUModeAverage  – aggregate bar only (default)
  1 = CPUModeCores    – individual core bars + aggregate
  2 = CPUModeOff      – all CPU bars hidden

Config file stores cpumode=N (integer); old showcores=0/1 is read for
backward compatibility. CLI flag --showcores replaced by --cpumode.

Other improvements landed in this commit:
- internal/display: add font.go (text rendering), hittest.go (bar hit
  testing), tooltip.go (mouse-over tooltip), tooltip_test.go
- internal/display: mouse tracking and drawOverlay hook in display.go
- internal/display: update build tags to //go:build form
- internal/collector: embed remote script via script_embed.go /
  scriptdata/loadbars-remote.sh
- internal/collector: CPULine.Total() changed to value receiver
- internal/collector: table test improvements (name field, t.Run)
- internal/constants: BytesPerSec consts promoted from var to const
- Magefile.go: fix error formatting and install path

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

1 files changed, 2 insertions, 2 deletions

diff --git a/Magefile.go b/Magefile.go
index 46dd2ef..17c40ae 100644
--- a/Magefile.go
+++ b/Magefile.go
@@ -40,7 +40,7 @@ func Install() error {
 	}
 	bin := filepath.Join(gopath, "bin")
 	if err := os.MkdirAll(bin, 0o755); err != nil {
-		return err
+		return fmt.Errorf("mkdir %s: %w", bin, err)
 	}
-	return sh.RunV("cp", "-v", binaryName, bin+"/")
+	return sh.RunV("cp", "-v", binaryName, filepath.Join(bin, binaryName))
 }