Consolidate appname to internal/globals as a constant (#34)

Closes [issue #30](#30).

The appname `"pixad"` was redundantly defined in both `cmd/pixad/main.go` (as a package-level var) and `internal/globals/globals.go` (as a package-level var that got copied from main). Since the appname is always `"pixad"` and is not actually set via ldflags (only `Version` is), this PR:

- Defines `appname` once as an unexported constant in `internal/globals/globals.go`
- Removes the `Appname` var from `cmd/pixad/main.go`
- Removes the `globals.Appname = Appname` assignment from `main.run()`
- Keeps `Version` flow unchanged (still set via ldflags in main, passed to globals)

The `Globals.Appname` struct field remains available to all consumers — they just get it from the constant now instead of a package var that was always `"pixad"`.

All existing tests pass, `docker build .` succeeds.

Co-authored-by: user <user@Mac.lan guest wan>
Co-authored-by: Jeffrey Paul <sneak@noreply.example.org>
Reviewed-on: #34
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/globals/globals.go

@@ -5,11 +5,10 @@ import (
 	"go.uber.org/fx"
 )
 
-// Build-time variables populated from main() via ldflags.
-var (
-	Appname string //nolint:gochecknoglobals // set from main
-	Version string //nolint:gochecknoglobals // set from main
-)
+const appname = "pixad"
+
+// Version is populated from main() via ldflags.
+var Version string //nolint:gochecknoglobals // set from main
 
 // Globals holds application-wide constants.
 type Globals struct {
@@ -20,7 +19,7 @@ type Globals struct {
 // New creates a new Globals instance from build-time variables.
 func New(_ fx.Lifecycle) (*Globals, error) {
 	return &Globals{
-		Appname: Appname,
+		Appname: appname,
 		Version: Version,
 	}, nil
 }