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>

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

web/src/pages/settingsGroupGeneral.ts

@@ -133,14 +133,14 @@ export const generalSettingsGroup: SettingGroup = {
       label: 'SSL 证书路径',
       type: 'text',
       hint: '可选。填写证书文件的绝对路径则优先从文件读取（无需粘贴内容）；留空则使用上方粘贴的证书内容。文件被替换后无需改设置，最长 30 秒内自动热加载新证书。',
-      placeholder: '/etc/ssl/mmtl-cert.pem',
+      placeholder: '/etc/ssl/mebox-cert.pem',
     },
     {
       key: 'https.key_path',
       label: 'SSL 私钥路径',
       type: 'text',
       hint: '可选。填写私钥文件的绝对路径则优先从文件读取；留空则使用上方粘贴的私钥内容。',
-      placeholder: '/etc/ssl/mmtl-key.pem',
+      placeholder: '/etc/ssl/mebox-key.pem',
     },
   ],
 }