Real-time DeepSeek V4 API peak/off-peak status widget

Key features

• Pill (always visible, in the session header next to the Session log button).
• The PEAK pill in the session header, the BALANCE row with the REFRESH and TOP UP actions, and the per-model 30-day peak/off-peak bar charts (v4-pro and v4-flash).
• The schedule and the pre-cutover date are baked in as constants in src/client/domain.ts.
• Reads the current phase from the browser clock against a baked-in UTC schedule
• Red during peak windows (2× the off-peak rate)