feat(ui): multi-installation aware settings UI (#283 PR 4/7)

integration page (settings/integration):
- loader returns githubAppLinks[] array with installation status
- action refactored to discriminated union + parseWithZod + match (CLAUDE.md 規約)
- new INTENTS: disconnectGithubAppLink, confirmDisconnectGithubAppLink
- per-installation disconnect with assertInstallationBelongsToOrg validation

GitHub App section UI:
- InstallationCard renders one card per active installation
- per-installation fetcher + ConfirmDialog (preserves installationId)
- "Add another GitHub account" button when at least one link exists
- buildInstallationSettingsUrl branches by github_account_type (User → /settings/installations/<id>, Organization → /organizations/<login>/settings/installations)

repositories.add page:
- installation selector via shared <InstallationSelect> when 2+ active links
- per-installation fetchAllInstallationRepos cache key
- loader/action share resolveInstallationIdForApp helper for installation resolution
- assertInstallationBelongsToOrg server-side validation
- addRepository mutation accepts githubInstallationId + upsertRepositoryMembership

github-users page:
- loader returns installationOptions via shared getActiveInstallationOptions
- searchGithubUsers accepts installationId, validates via assertInstallationBelongsToOrg
- toolbar uses shared <InstallationSelect>; selection persisted in URL searchParams
- Add button disabled when 2+ installations and none selected (UX feedback)

shared helpers added:
- app/libs/github-account.ts: formatGithubAccountLabel, isPersonalAccount, buildInstallationSettingsUrl
- app/components/installation-select.tsx: <InstallationSelect> reusable component
- app/services/github-integration-queries.server.ts: getActiveInstallationOptions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: coji

app/libs/github-account.ts

@@ -0,0 +1,32 @@
+/**
+ * Shared formatting / URL helpers for GitHub App installation links.
+ */
+
+export type GithubAccountLike = {
+  installationId: number
+  githubOrg: string
+  githubAccountType: string | null
+}
+
+export const isPersonalAccount = (link: GithubAccountLike): boolean =>
+  link.githubAccountType === 'User'
+
+/**
+ * UI label for an installation account. Personal accounts get an `@` prefix
+ * (matching GitHub's own convention) while organizations show their bare login.
+ */
+export const formatGithubAccountLabel = (link: GithubAccountLike): string =>
+  isPersonalAccount(link) ? `@${link.githubOrg}` : link.githubOrg
+
+/**
+ * GitHub-side settings URL for managing this installation.
+ *
+ * - Personal: `https://github.com/settings/installations/<id>`
+ * - Organization: `https://github.com/organizations/<login>/settings/installations`
+ */
+export const buildInstallationSettingsUrl = (
+  link: GithubAccountLike,
+): string =>
+  isPersonalAccount(link)
+    ? `https://github.com/settings/installations/${link.installationId}`
+    : `https://github.com/organizations/${encodeURIComponent(link.githubOrg)}/settings/installations`