chore: upgrade ESLint toolchain to v10

Upgrades all ESLint-related packages to their next major versions:

- eslint: ^9.39.3 → ^10.0.2
- @eslint/js: ^9.39.3 → ^10.0.1
- @eslint/compat: ^1.4.1 → ^2.0.2
- eslint-plugin-svelte: ^2.46.1 → ^3.15.0
- svelte-eslint-parser: ^0.43.0 → ^1.5.1
- globals: ^15.15.0 → ^17.3.0
- eslint-config-eslint: removed (was unused — not imported in eslint.config.js)

No changes to eslint.config.js were needed:
- The project already uses flat config format (eslint.config.js), so the
  'old config format no longer supported' breaking change does not apply.
- The --ignore-pattern CLI flag is still supported in v10.
- No new rules from eslint:recommended triggered errors in this codebase.

All checks pass:
- svelte-check: 0 errors, 0 warnings
- build: success
- lint: success (Prettier + ESLint v10)

Closes #171
Part of epic #174

Author: josecelano