Localization: add Spanish translation

[codebounty-local-platformapp]

Problem

TaskForge is English-only. First step toward i18n is a single non-English locale.

Proposed solution

• Extract user-facing strings into a small dictionary.
• Add es locale.
• Detect via navigator.language, allow override.

A bounty has been opened for this issue on CodeBounty.

[blankcw]

Hi, I'd like to work on this issue. I have a small implementation ready that adds an en/es translation dictionary, detects Spanish via navigator.language, supports ?lang=es / ?lang=en overrides, and localizes the current static and dynamic UI text.