ATELIER: warm porcelain UI with real-state overview and node cards

[lop-spec]

Scope

• UI-only implementation of the selected ATELIER design across all seven views; real current-node metrics and explicit historical/empty states.
• Responsive layout, keyboard node selection, separate probe buttons, offline fonts/SVG.
• Based directly on stable main e1e5386; deliberately excludes the unfinished parallel-SSE changes in draft Parallel SSE-only network quality (draft: 20s end-to-end gate not met) #3. Existing network/core/subscription behavior is unchanged.
• Read-only fixture preview, 8 new UI tests (95 tests passing on stable baseline); verified CI EXE retained for safe local UI handoff.

No credentials, live configuration, or runtime state included.