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/cloud/emby.go

@@ -21,7 +21,7 @@ import (
 
 // embyProvider implements Provider against a remote Emby server using an
 // api_key (token) for authentication. DirectLink.Resolve returns the remote
-// stream URL; whether MMTL reverse-proxies the bytes is decided by the
+// stream URL; whether MeBox reverse-proxies the bytes is decided by the
 // emby.proxy_play account config (defaults to off).
 type embyProvider struct {
 	base      string // e.g. http://host:8096（自动补 /emby 前缀）
@@ -159,7 +159,7 @@ func (p *embyProvider) ensureToken(ctx context.Context) (string, error) {
 		return "", err
 	}
 	req.Header.Set("Content-Type", "application/json")
-	req.Header.Set("X-Emby-Authorization", `MediaBrowser Client="MMTL", Device="MMTL-Federated", DeviceId="mmtl-federated", Version="1.0"`)
+	req.Header.Set("X-Emby-Authorization", `MediaBrowser Client="MeBox", Device="MeBox-Federated", DeviceId="mebox-federated", Version="1.0"`)
 	resp, err := p.client.Do(req)
 	if err != nil {
 		return "", err
@@ -234,7 +234,7 @@ func (p *embyProvider) List(ctx context.Context, dirID string) ([]FileEntry, err
 }
 
 // Resolve 返回远程 Emby 直链。Proxy=true 时由调用方(StrmService.ProxyDirect)
-// 反向代理流量；false 时 302 到直链。默认不代理（播放字节不经过 MMTL）。
+// 反向代理流量；false 时 302 到直链。默认不代理（播放字节不经过 MeBox）。
 func (p *embyProvider) Resolve(ctx context.Context, fileRef string) (*DirectLink, error) {
 	token, err := p.ensureToken(ctx)
 	if err != nil {