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/bangumi.go

@@ -23,7 +23,7 @@ import (
 
 	"go.uber.org/zap"
 
-	"github.com/ShukeBta/MMTL/internal/config"
+	"github.com/truewhile/MeBox/internal/config"
 )
 
 // BangumiProvider talks to https://api.bgm.tv.
@@ -181,7 +181,7 @@ func (b *BangumiProvider) getJSON(ctx context.Context, u string, out any) error
 	if err != nil {
 		return err
 	}
-	req.Header.Set("User-Agent", "MMTL/0.1 (https://github.com/ShukeBta/MMTL)")
+	req.Header.Set("User-Agent", "MeBox/0.1 (https://github.com/truewhile/MeBox)")
 	if t := strings.TrimSpace(b.cfg.Secrets.BangumiToken); t != "" {
 		req.Header.Set("Authorization", "Bearer "+t)
 	}