WhatIf: grid connection export limit, independent of battery

[springfall2008]

Summary

• Adds export_limit_kw as a top-level WhatIf (annual prediction) config field, defaulting to 10kW - the property's grid-connection export cap, combined via min() with whatever apply_hardware() already derives for export capability (the battery's inverter, or summed solar kWp for a PV-only run).
• Previously this only existed as battery.export_limit_kw, so a battery-less run had no way to model a grid export cap at all. It's still read as a legacy fallback so existing hand-written YAML configs and previously stored runs keep behaving the same.
• Web form: moved the "Export limit" field out of the Battery fieldset into its own "Grid connection" fieldset so it's visibly independent of whether a battery is configured; prefill now reads the live instance's real export_limit setting into this field.
• No CLI flag changes needed - annual_cli.py just feeds YAML into validate_config(), so the new key works from the command line automatically.
• Docs updated in docs/annual-prediction.md.

Test plan

• ./run_all --test annual_config --test annual_bootstrap --test web_annual passes
• ./run_all --quick passes (full suite, including annual_scenarios, annual_job, annual_cli_machine_end_to_end)
• ./run_pre_commit passes (ruff, black, cspell, markdownlint)

🤖 Generated with Claude Code

[Copilot]

🟡 Changes recommended

The new validation rejects export_limit_kw: 0, which is a backward-incompatible behavior change (legacy configs could previously accept 0) and removes the ability to model “no export allowed.”

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR updates the annual “WhatIf” (offline/annual prediction) configuration to support a top-level export_limit_kw representing the grid connection export cap, so PV-only runs can model an export limit even when no battery is configured. It also updates the web UI to present this as independent of the battery, maintains a legacy fallback for older configs, and updates unit tests and docs accordingly.

Changes:

• Add/validate top-level export_limit_kw in annual config (with legacy fallback from battery.export_limit_kw) and apply it as a min() cap in apply_hardware().
• Update the annual web form to move “Export limit” into a new “Grid connection” fieldset and prefill it from the live instance’s export limit setting.
• Update docs and tests to reflect the new config shape and behavior.

File summaries

File	Description
docs/annual-prediction.md	Documents new top-level export_limit_kw and legacy compatibility.
apps/predbat/web_annual.py	Moves export limit to top-level grid field, updates prefill/post handling and run details rendering.
apps/predbat/annual.py	Introduces DEFAULT_EXPORT_LIMIT_KW, validates export_limit_kw, and applies it as a grid cap in apply_hardware().
apps/predbat/tests/test_web_annual.py	Updates form POST expectations and verifies export limit default/prefill behavior.
apps/predbat/tests/test_annual_config.py	Adds coverage for new top-level key, legacy fallback, precedence, and PV-only behavior.
apps/predbat/tests/test_annual_bootstrap.py	Updates apply_hardware() calls and adds scenarios validating export cap clipping behavior.

Review details

• Files reviewed: 6/6 changed files
• Comments generated: 1
• Review effort level: Lite

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