feat(sub): auto-detect subscription format by User-Agent (Updated) (#5826)

* feat(settings): add subscription format controls

* feat(sub): auto-detect subscription formats

* fix(xray): validate balancer regexes before save

* Revert "fix(xray): validate balancer regexes before save"

This reverts commit 8a208ce71b.

* doc(endpoints): align indent spaces

* doc(settings): improve error message formatting in validateSubUserAgentRegex

- Use NewErrorf with proper formatting instead of NewError with string concatenation
- Add comment explaining the rationale for returning original pattern value
- This preserves the intentional design where empty input is stored as empty
  in the DB and inherited as the runtime default at read time

---------

Co-authored-by: Tomilla <5007859+Tomilla@users.noreply.github.com>
Co-authored-by: Sanaei <ho3ein.sanaei@gmail.com>

internal/web/translation/en-US.json

@@ -1310,6 +1310,19 @@
       "subJsonEnable": "Enable/Disable the JSON subscription endpoint independently.",
       "subJsonEnableTitle": "JSON subscription",
       "subClashEnableTitle": "Clash / Mihomo subscription",
+      "subFormatsTipTitle": "Format-specific subscription settings",
+      "subFormatsTipDesc": "Configure JSON and Clash / Mihomo URL paths, reverse URLs, and client auto-detection separately.",
+      "subFormatsTipAction": "Open Sub Formats",
+      "subJsonAutoDetect": "Auto-detect Xray JSON clients",
+      "subJsonAutoDetectDesc": "When enabled, recognized compatible clients requesting the standard subscription URL receive an Xray JSON configuration array automatically. Other clients keep the raw/base64 response. Requires JSON subscription to be enabled and a panel restart to apply.",
+      "subJsonAlwaysArray": "Always return a JSON array",
+      "subJsonAlwaysArrayDesc": "Return the explicit JSON subscription endpoint as an array even when it contains one profile, as required by the XTLS subscription standard. Auto-detected JSON responses always use arrays. Leave disabled to preserve the legacy single-object response.",
+      "subJsonUserAgentRegex": "Xray JSON User-Agent regex",
+      "subJsonUserAgentRegexDesc": "Go RE2 regular expression matched against the client's User-Agent to auto-select the Xray JSON format on the standard subscription URL. Empty by default, so auto-detection stays off until you set a pattern for the clients you want to serve. Other clients keep the raw/base64 response. Restart the panel after changes.",
+      "subClashAutoDetect": "Auto-detect Clash/Mihomo clients",
+      "subClashAutoDetectDesc": "When enabled, recognized Clash/Mihomo clients requesting the standard subscription URL receive Clash YAML automatically. Browsers still show the subscription page, other clients keep the raw/base64 response, and the explicit JSON and Clash URLs remain available. Requires Clash/Mihomo subscription to be enabled and a panel restart to apply.",
+      "subClashUserAgentRegex": "Clash/Mihomo User-Agent regex",
+      "subClashUserAgentRegexDesc": "Go RE2 regular expression matched against the client's User-Agent to recognize Clash/Mihomo clients on the standard subscription URL. Leave empty to use the default pattern. Restart the panel after changes.",
       "subTitle": "Subscription Title",
       "subTitleDesc": "Title shown in VPN client",
       "subSupportUrl": "Support URL",
@@ -1400,7 +1413,7 @@
       },
       "subFormats": {
         "finalMask": "Final Mask",
-        "finalMaskDesc": "xray finalmask masks (TCP/UDP) and QUIC tuning injected into every JSON subscription stream. Requires a recent xray client.",
+        "finalMaskDesc": "Inject Xray finalmask TCP/UDP masks and QUIC parameters into every generated Xray JSON profile. Requires a client app that supports Xray JSON subscriptions and a recent Xray core.",
         "packets": "Packets",
         "length": "Length",
         "interval": "Interval",