feat: OTA 自更新（Gitea Release 为更新源）

- update.rs：检查最新 Release（latest 端点+列表回退）、版本比较、
  平台产物挑选（含 .sha256 侧车）、下载进度、sha256 校验、
  自替换（改名 .old → 换入新 exe → 拉起新进程）、启动清理遗留
- 设置 → 关于：检查更新按钮、发现新版本提示、下载进度条（Progress）、
  失败重试；自动检查更新开关真正生效（启动后台检查并弹通知）
- 版本 1.0.0 → 1.0.1（首个带 OTA 的发布版本）
- 顺手修 clippy 遗留警告（is_none_or、合并 if）

Cargo.lock

@@ -4065,7 +4065,7 @@ dependencies = [
 
 [[package]]
 name = "mqttx-desktop"
-version = "1.0.0"
+version = "1.0.1"
 dependencies = [
  "anyhow",
  "base64 0.22.1",
@@ -4081,8 +4081,10 @@ dependencies = [
  "serde",
  "serde_json",
  "sha1",
+ "sha2 0.10.9",
  "smol",
  "tokio",
+ "ureq",
  "uuid",
 ]
 
@@ -5950,6 +5952,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0d41d731c7d2f962d1ccc364cec258de3c0e93b38c2fb3ba97ac74513048d634"
 dependencies = [
  "aws-lc-rs",
+ "log",
  "once_cell",
  "ring",
  "rustls-pki-types",
@@ -7379,6 +7382,24 @@ version = "0.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8ecb6da28b8a351d773b68d5825ac39017e680750f980f3a1a85cd8dd28a47c1"
 
+[[package]]
+name = "ureq"
+version = "2.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "02d1a66277ed75f640d608235660df48c8e3c19f3b4edb6a263315626cc3c01d"
+dependencies = [
+ "base64 0.22.1",
+ "flate2",
+ "log",
+ "once_cell",
+ "rustls",
+ "rustls-pki-types",
+ "serde",
+ "serde_json",
+ "url",
+ "webpki-roots 0.26.11",
+]
+
 [[package]]
 name = "url"
 version = "2.5.8"
@@ -7789,6 +7810,24 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "webpki-roots"
+version = "0.26.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "521bc38abb08001b01866da9f51eb7c5d647a19260e00054a8c7fd5f9e57f7a9"
+dependencies = [
+ "webpki-roots 1.0.9",
+]
+
+[[package]]
+name = "webpki-roots"
+version = "1.0.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7dcd9d09a39985f5344844e66b0c530a33843579125f23e21e9f0f220850f22a"
+dependencies = [
+ "rustls-pki-types",
+]
+
 [[package]]
 name = "weezl"
 version = "0.1.12"