Bug Fixes

• cost-analysis: price Octopus tariffs, keep rate history, report unpriced energy (06f7e7b)
• reporting: derive transaction energy from the row's meter delta, and repair stored values (09c80c1)
• transactions: a session ends at its unplug, never after the next session starts (f6cf590)
• cost-analysis: read a session's meter window to the first sample after its end (684b44c)
• summary: return total session minutes and open sessions (b087dfe)
• statistics: energy-weighted bucket power; success rate over settled sessions only (0a8a62c)