chore: migrate self-distribution links from GitHub to self-hosted Gitea

GitHub accounts suspended; all first-party distribution now served from
git.881218.xyz/rogue/NexusGate (Gitea):
- raw:  /rogue/NexusGate/raw/branch/<branch>/<path>
- release assets and source archives under the same repo path
- scripts gain a GIT_BASE variable built from NG_REPO (default
  rogue/NexusGate); NG_REPO/NG_BRANCH/--repo/--branch semantics unchanged
- panel enrollment/uninstall commands in public/app.js point at Gitea raw
- install.sh/nexusgate.sh/agent-singbox.sh stats source previously
  defaulted to the upstream repo (a2899882); defaults now this repo
Upstream dependency references (sagernet/sing-box Go module) untouched.

scripts/agent-update.sh

@@ -1,9 +1,11 @@
 #!/usr/bin/env bash
 set -Eeuo pipefail
 
-REPO="${NG_REPO:-aaaamoooo/NexusGate}"
+REPO="${NG_REPO:-rogue/NexusGate}"
 BRANCH="${NG_BRANCH:-main}"
-# Go agent 二进制所在的 GitHub Release tag（与 agent-install.sh 保持一致）
+# 自建 Gitea 分发基址（raw / release 均由此拼装）
+GIT_BASE="https://git.881218.xyz/${REPO}"
+# Go agent 二进制所在的 Gitea Release tag（与 agent-install.sh 保持一致）
 AGENT_RELEASE="${NG_AGENT_RELEASE:-agent-v0.6.8}"
 die() { printf '错误：%s\n' "$*" >&2; exit 1; }
 info() { printf '\033[1;36m[NexusGate Agent]\033[0m %s\n' "$*"; }
@@ -27,7 +29,7 @@ TARGET_IMPL="go"
 info "当前 Agent 实现：${CURRENT_IMPL}；更新目标：${TARGET_IMPL}"
 
 raw_fetch() {
-  curl -fL --retry 3 "https://raw.githubusercontent.com/${REPO}/${BRANCH}/$1" -o "$2"
+  curl -fL --retry 3 "${GIT_BASE}/raw/branch/${BRANCH}/$1" -o "$2"
 }
 
 agent_arch() {
@@ -45,7 +47,7 @@ fetch_agent_binary() {
   if [[ -n "${NG_LOCAL_SRC:-}" && -f "${NG_LOCAL_SRC}/agent-go/nexusgate-agent-linux-${arch}" ]]; then
     cp -a "${NG_LOCAL_SRC}/agent-go/nexusgate-agent-linux-${arch}" "$out"
   else
-    curl -fL --retry 3 "https://github.com/${REPO}/releases/download/${AGENT_RELEASE}/nexusgate-agent-linux-${arch}" -o "$out"
+    curl -fL --retry 3 "${GIT_BASE}/releases/download/${AGENT_RELEASE}/nexusgate-agent-linux-${arch}" -o "$out"
   fi
   [[ -s "$out" ]] || die 'Agent 二进制下载不完整'
 }