fix(xhttp): stop injecting scMaxEachPostBytes/scMinPostsIntervalMs defaults (#5141)

The panel seeded xhttp configs with scMaxEachPostBytes=1000000 and
scMinPostsIntervalMs=30 — xray-core''s own defaults — and emitted them
into every generated config and share link. The literal
scMinPostsIntervalMs=30 is a stable DPI fingerprint that Russia''s TSPU
keys on to block connections on mobile networks.

New configs no longer seed these values (empty schema/template defaults,
so xray-core applies its internal defaults). For configs already stored
with the old defaults, the link/subscription builders now drop values
equal to xray-core''s defaults instead of advertising them — covering
panel share links, the raw subscription, and the JSON subscription
without requiring every inbound to be re-saved. Non-default values the
user set deliberately are still emitted.

frontend/src/test/__snapshots__/stream.test.ts.snap

@@ -47,8 +47,8 @@ exports[`NetworkSettingsSchema fixtures > parses xhttp-basic byte-stably 1`] = `
     "noSSEHeader": false,
     "path": "/sp",
     "scMaxBufferedPosts": 30,
-    "scMaxEachPostBytes": "1000000",
-    "scMinPostsIntervalMs": "30",
+    "scMaxEachPostBytes": "",
+    "scMinPostsIntervalMs": "",
     "scStreamUpServerSecs": "20-80",
     "seqKey": "",
     "seqPlacement": "",
@@ -81,8 +81,8 @@ exports[`NetworkSettingsSchema fixtures > parses xhttp-extra-padding byte-stably
     "noSSEHeader": false,
     "path": "/sp",
     "scMaxBufferedPosts": 30,
-    "scMaxEachPostBytes": "1000000",
-    "scMinPostsIntervalMs": "30",
+    "scMaxEachPostBytes": "",
+    "scMinPostsIntervalMs": "",
     "scStreamUpServerSecs": "20-80",
     "seqKey": "",
     "seqPlacement": "",
@@ -115,8 +115,8 @@ exports[`NetworkSettingsSchema fixtures > parses xhttp-extra-placement byte-stab
     "noSSEHeader": false,
     "path": "/sp",
     "scMaxBufferedPosts": 30,
-    "scMaxEachPostBytes": "1000000",
-    "scMinPostsIntervalMs": "30",
+    "scMaxEachPostBytes": "",
+    "scMinPostsIntervalMs": "",
     "scStreamUpServerSecs": "20-80",
     "seqKey": "X-Seq",
     "seqPlacement": "cookie",