The terminal's System screen draws the machine's CPU, memory and load over the last 6 hours as one sparkline each, as MCP `telemetry_history` reads them #7321

Intent: the owner sees at a glance whether the machine is calm, without leaving the terminal.

Done:

• [ ] The System screen (src/tui/screens/system.ts) shows three lines (CPU, memory, load), each a sparkline of historyFor (src/system/telemetry.ts) over the last 6 hours, with the latest value and the peak in words.
• [ ] h cycles the window 1 h / 6 h / 24 h / 72 h, as the MCP tool's hours does.
• [ ] No history yet says no readings yet, never an empty chart.
• [ ] Only those the MCP tool lets read telemetry see it; anyone else sees no line.
• [ ] test/tui-system.test.ts gains a case with recorded points that sees the three lines and one that sees the refusal.

Files: src/tui/screens/system.ts, test/tui-system.test.ts. Risk: #7296's pull also edits this screen; add a section below what it draws.