Simplify config flow UI text

[florianhorner]

Summary

Rewrites the config flow UI text across all 3 translation files (en, pt-BR, sk) to be concise and scannable:

• Shorter labels: "Device name" → "Name", "Controlled lights" → "Select lights", "Brightness mapping" → "Brightness curve"
• Trimmed descriptions: Verbose paragraph-length helper text replaced with one-line tooltips
• Removed filler: "Please provide a name for the Lightener device you are creating" → field label speaks for itself
• Fixed Slovak: Untranslated English string "Current brightness" now properly translated

Before vs After (English)

Element	Before	After
Step 1 title	"Create a Lightener device"	"New Lightener device"
Name hint	40-word paragraph	"A room or area name works best, e.g. "Living Room""
Light selector label	"Select the light entities to be controlled by this Lightener device"	"Lights to control"
Mapping helper	50-word paragraph	"One mapping per line as group:light. Example: "60:100" means at 60% group brightness, this light reaches 100%."

No Python changes — purely translation/copy improvements.

Context

This is a low-risk incremental step toward the broader UX improvements discussed in #147 and #117. While those issues call for structural changes (visual curve editor, single-screen config), this PR reduces cognitive load in the existing flow by cleaning up the copy.

Notes

• pt-BR and sk translations are best-effort — native speaker review welcome
• All placeholder variables ({light_name}, {current_brightness}, {error_entry}) preserved
• JSON structure unchanged; no config_flow.py modifications

Test plan

• Install integration, run config flow — verify all 3 steps render correctly
• Edit an existing Lightener device via options flow — verify labels match
• Trigger validation error on brightness mapping — verify error message renders with {error_entry} placeholder
• Switch HA language to pt-BR and sk — verify translations render

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