feat: EV priority Home Assistant blueprint

[XavierBerger]

Summary

• Adds blueprints/priority_to_ev.yaml, a Home Assistant blueprint that gives the EV charger priority over the Solar Router's diversion load whenever there is enough solar surplus to run the EV, and reactivates the router once the EV is full or unplugged.
• Ships the reference doc as docs/en/blueprint_priority_to_ev.md (with French stub) and a corrected truth-table page docs/en/blueprint_use_cases.md; both wired into mkdocs.yml.
• Adds a top-level AGENTS.md describing the project's layout, package system, and conventions for AI assistants working on the repo.

Design decisions

• numeric_state triggers list both grid_power and diverted_power in entity_id. Home Assistant only re-evaluates the template when a listed entity changes — the classic blueprint pitfall is to list only the grid sensor, in which case a rising diverted value with a flat grid never re-fires the trigger. Both entities are listed so every surplus change is observed.
• Anti-flicker ev_soc guard. Once ev_soc >= ev_full_soc (default 100 %), Condition 1 is blocked and the router is not deactivated. This is what makes the "never stop at full" behaviour actually happen in code. Users without an SOC sensor can raise ev_full_soc to 101 % to disable the guard.
• mode: queued, max: 2 avoids the sunrise-recovery race in which both numeric-state triggers cross their thresholds simultaneously and one is dropped under mode: single.
• Plug/unplug debounce. ev_connected state triggers use for: !input delay_before_deactivation / delay_before_activation, so a connector wiggle can't slam the router.
• has_value(...) guards on the surplus template and Condition 1 treat sensor drop-outs as 0 W surplus rather than 0-substituted phantom surplus that could spuriously deactivate the router.
• homeassistant.min_version: 2024.8.0 pinned for action: keys, trigger_variables + !input, and has_value().

Docs

• docs/en/blueprint_priority_to_ev.md — full algorithm, worked "day in the life" example, and a Known-behavior section covering overnight lockout, sensor drop-outs, plug debounce, SOC unavailability, and reload semantics.
• docs/en/blueprint_use_cases.md — corrected truth table (a prior draft had row 5 vs row 7 diverging on identical inputs, row 10 acting on a surplus below ev_full_threshold, and row 11 arithmetic inconsistent with the shown numbers).
• French stubs added under docs/fr/; mkdocs.yml nav updated for both locales.

Test plan

• Import the blueprint into Home Assistant and confirm all inputs render.
• Walk a scripted state sequence covering every row of the truth table (particularly rows 5/7/10/11/12 and boundary rows 13/14).
• Force diverted_power to unavailable mid-run and confirm the router does not flip.
• mkdocs serve locally and confirm the new pages appear under both /en/ and /fr/ navs.

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