feat: add unit converter tools

[Bpr3]

Add New “Conversion Tools” Category with 11 Unit Converters

Summary

Introduces a brand new Conversion Tools category plus a unified, DRY architecture for unit conversion utilities.

Included Converters
Length • Area • Volume • Mass • Temperature • Speed • Digital Storage • Energy • Voltage • Current • Power

Key Changes

• Added conversion category (i18n + category config + icon)
• Added meta + component for each converter (e.g. energy-converter-meta.ts, voltage-converter-meta.ts)
• Implemented a GenericConverter component (shared logic/UI: inputs, unit selectors, expert mode, copy)
• Expert mode exposes full unit lists; classic mode shows curated common units
• Removed obsolete measurement/conversion legacy JSON files
• Updated i18n (all converter names, descriptions, shortDescriptions)
• Ensured unique, meaningful icons (e.g. energy: mdi:solar-power, voltage: mdi:flash)

Architecture

• Each tool = lightweight wrapper passing config (classic units, defaults) into GenericConverter
• Meta files use defineTool for consistent typing (path, icon, keywords, i18n)
• Category integration handled via tools/index.ts and categoriesConfig

Testing Instructions

• Open /categories/conversion
• Verify all 11 converters list and load
• Toggle Expert Mode (only appears when > classic unit set)
• Change units and confirm instant conversion
• Use copy button on result field
• Check i18n strings (titles/descriptions) render correctly