Migrate dependencies to Gradle Version Catalog

[Copilot]

All dependency versions were scattered across multiple build.gradle.kts files and gradle.properties. This migrates everything to a single gradle/libs.versions.toml Version Catalog.

Changes

• gradle/libs.versions.toml — new catalog defining all versions, library coordinates, and plugin IDs in one place
• Gradle wrapper — bumped 6.8 → 7.6.1; Version Catalogs require ≥ 7.0 (stable from 7.4)
• All build.gradle.kts files — replaced hardcoded strings and $ktor_version/$kotlin_version interpolation with typed catalog accessors; plugin declarations use alias()
• gradle.properties — removed ktor_version and kotlin_version (now owned by the catalog)
• kotest — standardized to 5.4.2 across all modules (core had a stale 4.6.2)

Before / After

// Before
val ktor_version: String by project
implementation("io.ktor:ktor-client-cio-jvm:$ktor_version")
testImplementation("io.kotest:kotest-runner-junit5:5.4.2")

// After
implementation(libs.ktor.client.cio)
testImplementation(libs.kotest.runner.junit5)

Original prompt

перегони зависимости в version catalog

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