feat(web,ui): per-provider git forge API base URL and detection URLs

Configure a default API base URL per git provider (github/gitlab/gitea)
in settings.json gitProviders, with GitHub Enterprise support (Octokit
baseUrl + device-flow web origin derived from the API base), and replace
the client-side custom-domains list with server-persisted detection URL
chips (SSH/HTTPS forms normalized to hosts). The configured API base host
auto-counts as a detection host. Settings round-trip through the existing
/api/config/settings sanitizer; the UI store hydrates from server settings
with a one-time localStorage migration.

packages/web/server/lib/github/repo/fork-detection.js

@@ -1,4 +1,7 @@
 import { resolveGitHubRepoFromDirectory } from './index.js';
+import { getProviderApiBaseUrl, githubWebOriginFromApiBase } from '../../git-providers/config.js';
+
+const getGitHubWebOrigin = () => githubWebOriginFromApiBase(getProviderApiBaseUrl('github'));
 
 const REPO_METADATA_TTL_MS = 5 * 60_000;
 const REPO_METADATA_CACHE_MAX_ENTRIES = 200;
@@ -75,7 +78,7 @@ export async function resolveRepoNetwork(octokit, directory, remoteName = 'origi
       result.push({
         owner: parent.owner.login,
         repo: parent.name,
-        url: parent.html_url || `https://github.com/${parent.owner.login}/${parent.name}`,
+        url: parent.html_url || `${getGitHubWebOrigin()}/${parent.owner.login}/${parent.name}`,
         source: 'upstream',
       });
     }
@@ -89,7 +92,7 @@ export async function resolveRepoNetwork(octokit, directory, remoteName = 'origi
       result.push({
         owner: source.owner.login,
         repo: source.name,
-        url: source.html_url || `https://github.com/${source.owner.login}/${source.name}`,
+        url: source.html_url || `${getGitHubWebOrigin()}/${source.owner.login}/${source.name}`,
         source: 'upstream',
       });
     }

packages/web/server/lib/github/repo/index.js

@@ -1,6 +1,17 @@
 import { getRemoteUrl } from '../../git/index.js';
+import { getProviderApiBaseUrl, githubWebOriginFromApiBase } from '../../git-providers/config.js';
 
-export const parseGitHubRemoteUrl = (raw) => {
+const getGitHubWebOrigin = () => githubWebOriginFromApiBase(getProviderApiBaseUrl('github'));
+
+const webHostFromOrigin = (webOrigin) => {
+  try {
+    return new URL(webOrigin).hostname || 'github.com';
+  } catch {
+    return 'github.com';
+  }
+};
+
+export const parseGitHubRemoteUrl = (raw, { host = 'github.com', webOrigin = 'https://github.com' } = {}) => {
   if (typeof raw !== 'string') {
     return null;
   }
@@ -10,34 +21,36 @@ export const parseGitHubRemoteUrl = (raw) => {
   }
 
   // git@github.com:OWNER/REPO.git
-  if (value.startsWith('git@github.com:')) {
-    const rest = value.slice('git@github.com:'.length);
+  const scpPrefix = `git@${host}:`;
+  if (value.startsWith(scpPrefix)) {
+    const rest = value.slice(scpPrefix.length);
     const cleaned = rest.endsWith('.git') ? rest.slice(0, -4) : rest;
     const [owner, repo] = cleaned.split('/');
     if (!owner || !repo) return null;
-    return { owner, repo, url: `https://github.com/${owner}/${repo}` };
+    return { owner, repo, url: `${webOrigin}/${owner}/${repo}` };
   }
 
   // ssh://git@github.com/OWNER/REPO.git
-  if (value.startsWith('ssh://git@github.com/')) {
-    const rest = value.slice('ssh://git@github.com/'.length);
+  const sshPrefix = `ssh://git@${host}/`;
+  if (value.startsWith(sshPrefix)) {
+    const rest = value.slice(sshPrefix.length);
     const cleaned = rest.endsWith('.git') ? rest.slice(0, -4) : rest;
     const [owner, repo] = cleaned.split('/');
     if (!owner || !repo) return null;
-    return { owner, repo, url: `https://github.com/${owner}/${repo}` };
+    return { owner, repo, url: `${webOrigin}/${owner}/${repo}` };
   }
 
   // https://github.com/OWNER/REPO(.git)
   try {
     const url = new URL(value);
-    if (url.hostname !== 'github.com') {
+    if (url.hostname !== host) {
       return null;
     }
     const path = url.pathname.replace(/^\/+/, '').replace(/\/+$/, '');
     const cleaned = path.endsWith('.git') ? path.slice(0, -4) : path;
     const [owner, repo] = cleaned.split('/');
     if (!owner || !repo) return null;
-    return { owner, repo, url: `https://github.com/${owner}/${repo}` };
+    return { owner, repo, url: `${webOrigin}/${owner}/${repo}` };
   } catch {
     return null;
   }
@@ -48,8 +61,10 @@ export async function resolveGitHubRepoFromDirectory(directory, remoteName = 'or
   if (!remoteUrl) {
     return { repo: null, remoteUrl: null };
   }
+  const webOrigin = getGitHubWebOrigin();
+  const host = webHostFromOrigin(webOrigin);
   return {
-    repo: parseGitHubRemoteUrl(remoteUrl),
+    repo: parseGitHubRemoteUrl(remoteUrl, { host, webOrigin }),
     remoteUrl,
   };
 }