Rebrand MMTL to MeBox (name, logo, Docker image) (#17)

* Rebrand MMTL to MeBox across codebase and assets

Rename the project display name, Go module path, environment variable
prefix (MEBOX_*), Docker image references, and UI branding from MMTL/mmtl
to MeBox/mebox. Replace logo assets with the new MeBox icon and keep
legacy SQLite migration support for existing mmtl.db deployments.

Co-authored-by: truewhile <truewhile@users.noreply.github.com>

* Fix logo icons: use cube-only crop without truncated text

Previous icon generation cropped too much of the source image, including
partial MeBox wordmark text that was cut off in square icon containers.
Regenerate logo-64/192/512, favicon, and SVG from cube-only region.

Co-authored-by: truewhile <truewhile@users.noreply.github.com>

---------

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: truewhile <truewhile@users.noreply.github.com>

internal/handler/emby_test_helpers_test.go

@@ -6,7 +6,7 @@ import (
 
 	"github.com/golang-jwt/jwt/v5"
 
-	"github.com/ShukeBta/MMTL/internal/middleware"
+	"github.com/truewhile/MeBox/internal/middleware"
 )
 
 func signedTestToken(t *testing.T, secret string) string {
@@ -23,7 +23,7 @@ func signedTestTokenWithPurpose(t *testing.T, secret, purpose string) string {
 		Purpose: purpose,
 		RegisteredClaims: jwt.RegisteredClaims{
 			ExpiresAt: jwt.NewNumericDate(time.Now().Add(time.Hour)),
-			Issuer:    "mmtl-test",
+			Issuer:    "mebox-test",
 			Subject:   "user-1",
 		},
 	}