feat(desktop): isolate platform accounts per desktop client

Scope desktop media accounts by the authenticated desktop client_id so
the same user logging in from Mac and Windows no longer sees a shared
account list. The list, identity lookup, upsert, patch, tombstone and
async health sink paths now all require matching client_id, and the
active uniqueness index moves from (workspace, platform, uid) to
(workspace, client, platform, uid).

Also strengthen the desktop client_id seed: when the OS machine id is
unavailable, fall back to a hashed fingerprint of stable hardware MAC
addresses before the random installation id, so the same hardware
keeps the same client across reinstalls.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/internal/tenant/repository/generated/querier.go

@@ -115,6 +115,7 @@ type Querier interface {
 	ListArticles(ctx context.Context, arg ListArticlesParams) ([]ListArticlesRow, error)
 	ListBrands(ctx context.Context, tenantID int64) ([]ListBrandsRow, error)
 	ListCompetitors(ctx context.Context, arg ListCompetitorsParams) ([]ListCompetitorsRow, error)
+	ListDesktopAccountsByClient(ctx context.Context, arg ListDesktopAccountsByClientParams) ([]ListDesktopAccountsByClientRow, error)
 	ListDesktopAccountsByUser(ctx context.Context, arg ListDesktopAccountsByUserParams) ([]ListDesktopAccountsByUserRow, error)
 	ListDesktopClientsByWorkspace(ctx context.Context, workspaceID int64) ([]DesktopClient, error)
 	ListImageAssets(ctx context.Context, arg ListImageAssetsParams) ([]ListImageAssetsRow, error)