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>

cmd/pixad/main.go

@@ -17,10 +17,7 @@ import (
 	"sneak.berlin/go/pixa/internal/server"
 )
 
-var (
-	Appname = "pixad" //nolint:gochecknoglobals // set by ldflags
-	Version string    //nolint:gochecknoglobals // set by ldflags
-)
+var Version string //nolint:gochecknoglobals // set by ldflags
 
 var configPath string //nolint:gochecknoglobals // cobra flag
 
@@ -40,7 +37,6 @@ func main() {
 }
 
 func run(_ *cobra.Command, _ []string) {
-	globals.Appname = Appname
 	globals.Version = Version
 
 	// Set config path in environment if specified via flag