docs: document sensor.tigo_max_power and Panel Power view in pv_production.md

[Copilot]

tigo.yaml defines three template sensors, but pv_production.md only documented two — omitting sensor.tigo_max_power used by the Page 3 "Panel Power" view, leaving setup instructions incomplete.

Changes to dashboards/pv_production.md

• Prerequisites table — added sensor.tigo_max_power (highest live _power across all 26 panels, in W)
• Views section — added View 3: Panel Power (/panel-power), describing the live power output display and its green color scale relative to sensor.tigo_max_power
• Tile Rendering section — added Page 3 color formula block:

  const max = parseFloat(states['sensor.tigo_max_power']?.state) || 1;
  const pct = Math.min(Math.max(val, 0) / max, 1);
  const alpha = pct * 0.7;
  // Green overlay: rgba(0, 220, 50, alpha)
  // Inner glow:    rgba(0, 255, 50, 0.8 * pct)

• YAML Structure table — added &pwr_tile_landscape and &pwr_tile_portrait anchor entries
• tigo.yaml code block — added Tigo Max Power sensor; corrected panel count from 24 → 26 throughout

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