follow-up: resolve remaining low findings from PR #1377

[Dumbris]

Remaining low-priority UX and consistency findings from PR #1377. Each item was verified during implementation or the final ZCode review and intentionally deferred from the merge.

• connect --all latency (cmd/mcpproxy/connect_notify.go, connect_cmd.go): notify is synchronous; daemon detection and HTTP-post budgets can add several seconds per client.
• Onboarding tab race (frontend/src/components/OnboardingWizard.vue): a delayed onOpened() result can overwrite a tab the user selected while its async load is pending.
• First-run dialog accessibility sizing (native/macos/MCPProxy/MCPProxy/Views/FirstRunDialog.swift): the fixed 460×300 frame may clip the added telemetry line under larger Dynamic Type settings.
• Client definition copy isolation (internal/connect/clients.go): GetAllClients/FindClient shallow-copy the new ClientInfoNames slice, allowing a future mutating caller to alter the global registry.
• Onboarding update callback constraint (internal/storage/manager.go, internal/storage/bbolt.go): document or redesign the mutator contract; re-entering Manager storage while the lock and bbolt write transaction are held can deadlock.
• Import secret placeholder coverage (internal/configimport/summary.go): classify embedded ${VAR} references and bare $VAR values, not only a whole-string ${VAR} placeholder.
• Disconnect reload guidance (frontend/src/components/ConnectModal.vue): render the returned reload hint after a disconnect.
• ConnectModal path presentation (frontend/src/components/ConnectModal.vue): use display_path instead of the unshortened config_path in the remaining row.
• Import apply response enrichment (internal/httpapi/import.go): recompute the direct REST apply response after credential overrides so it reflects the persisted values.
• CLI/REST empty-summary shape (cmd/mcpproxy/upstream_cmd.go): omit an empty summary key in CLI JSON to match REST for malformed stdio entries that lack both command and URL.
• macOS disconnect confirmation path (native/macos/MCPProxy/MCPProxy/Views/ConnectClientModel.swift): show the home-shortened display_path in the confirmation, consistent with the adjacent row and result view.