Feature: Native Solar Clipping Buffer (Resolves #1206)

[rholligan]

Resolves #1206. This PR introduces a native clipping buffer to Predbat. It prevents solar energy loss on high-generation days by reserving a dynamic buffer in the battery SoC, specifically targeting periods where PV generation is forecast to exceed inverter AC capacity or DNO export limits.

Key Features:

• Dynamic Buffer Calculation: Computes the required buffer (sensor.predbat_clipping_buffer_kwh) based on the solar forecast area exceeding the "Effective
  Clipping Limit" (choosing the most restrictive hardware or DNO constraint).
• Grid-Charge Capping: Restricts overnight grid charging to ensure headroom for the calculated buffer.
• Proactive Risk Management: Includes a two-stage safety system. It uses a risk_threshold (trigger) and a configurable clipping_buffer_safety_margin
  (default 5% of window solar) to protect against un-forecasted cloud-edge spikes.
• Dynamic Buffer Decay: Reserved space shrinks as the solar peak passes, releasing capacity for evening use.
• Web UI Integration: Adds a "Clipping Analysis" chart to the Predbat Web UI, displaying PV curves, clipping ceilings, and the decaying buffer.
• Improved Peak Reporting: Refined the clipping status text to report the actual high-risk generation period (minutes exceeding the limit) rather than the broad protection window, providing clearer information for the user.

Configuration Parameters:

• clipping_buffer_enable: Master toggle.
• clipping_buffer_forecast: Selection of forecast model (recommends pv_clearsky).
• clipping_buffer_safety_margin: Percentage of window solar to reserve as a safety factor (default 0.05).
• clipping_buffer_risk_threshold: Sensitivity factor to trigger the safety margin logic (default 0.80).
• clipping_buffer_can_discharge: Discharge behavior (None, Cost Optimal, or Always).
• clipping_buffer_min_kwh / max_kwh: Manual size constraints.
• clipping_buffer_limit_override: Manual power threshold override (Watts).

Testing & Documentation:

• Verified on live 5kW hardware; effectively mitigated 6.28kW solar spikes by holding battery headroom.
• Includes unit tests in apps/predbat/tests/test_clipping.py.
• Full feature documentation available in docs/clipping.md.

Developed with Gemini ✦

[tieskuh]

Cross-referencing #4023 (Model curtailment on a negative export price) — our PRs look complementary and touch some of the same files, so flagging for coordination.

	#4023	This PR (#4036)
Trigger	export price is negative (rate-conditional)	PV exceeds a power limit (inverter AC / DNO export)
Goal	avoid a phantom export cost + keep PV calibration clean	avoid solar lost to clipping
Approach	modelling-only (models the curtailment)	active control (reserves battery SoC headroom)
Related issue	#3986	#1206 (+ #3442 / #3481 / #3828)

Yours handles clipping against a power limit with active SoC buffering; mine models price-driven curtailment and keeps PV calibration clean (modelling-only). We overlap in prediction.py / solcast.py / output.py / config.py and the tests, so whichever merges second will need a rebase. Happy to rebase mine on top if yours lands first.