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/service/token_svc.go

@@ -12,9 +12,9 @@ import (
 	"github.com/golang-jwt/jwt/v5"
 	"go.uber.org/zap"
 
-	"github.com/ShukeBta/MMTL/internal/config"
-	"github.com/ShukeBta/MMTL/internal/model"
-	"github.com/ShukeBta/MMTL/internal/repository"
+	"github.com/truewhile/MeBox/internal/config"
+	"github.com/truewhile/MeBox/internal/model"
+	"github.com/truewhile/MeBox/internal/repository"
 )
 
 const (
@@ -150,7 +150,7 @@ func (s *TokenService) issueAccessToken(userID, role, tier string) (string, erro
 		RegisteredClaims: jwt.RegisteredClaims{
 			IssuedAt:  jwt.NewNumericDate(time.Now()),
 			ExpiresAt: jwt.NewNumericDate(time.Now().Add(AccessTokenDuration)),
-			Issuer:    "mmtl",
+			Issuer:    "mebox",
 			Subject:   userID,
 		},
 	}