Tariff: add time-based grid fees

[naltatis]

fixes #26164

Add ability to specify time-based (month, day, time) grid fees (e.g. for §14a Dynamische Netzentgelte). These can be combined with any price tariff.

• introduce chargesZones to overwrite existing charges for tariffs (advanced)
• reuse logic/structure/ui from existing zones feature
• add tariff preset to fixed tariff
• fixed tariff with chargesZones is treated as a dynamic tariff (preferred by planner, unlock cheap grid charging for lp and battery, show chart preview, ...)

Screenshot

[sourcery-ai]

Hey - I've left some high level feedback:

• The new ZoneSpec type is now shared between price zones and charge zones; consider renaming or separating the structs (e.g. PriceZoneSpec/ChargeZoneSpec) to avoid accidental cross‑use and make the semantics clearer at the call sites.
• In embed.effectiveCharges, you force timestamps to Local() before resolving zones; if tariffs should respect the original location on ts, it may be safer to rely on ts.Location() or document that all tariff time logic is explicitly local-time based.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The new `ZoneSpec` type is now shared between price zones and charge zones; consider renaming or separating the structs (e.g. `PriceZoneSpec`/`ChargeZoneSpec`) to avoid accidental cross‑use and make the semantics clearer at the call sites.
- In `embed.effectiveCharges`, you force timestamps to `Local()` before resolving zones; if tariffs should respect the original location on `ts`, it may be safer to rely on `ts.Location()` or document that all tariff time logic is explicitly local-time based.

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[andig]

Not sure I undestand. This is basically a UI wrapper for the fixed tariff?

[andig]

Whats the scope of these fees: any import/export tariff? Only on on fixed tariff?

[naltatis]

Not sure I undestand. This is basically a UI wrapper for the fixed tariff?

This is the ability to enter time-based grid fees for "all" price tariffs, import and export context.

In this process the fixed template also received the tariff-base preset so users with a constant energy price and dynamic grid fees dont have to recalculate all slots when the energy tariff changes it's regular price (see issue).
For fixed tariffs you could previously model this by using zones and calculate manually. For complex tariffs (api data) you previously had to use complex formula stuff. See examples in https://docs.evcc.io/en/docs/tariffs#custom-formulas