feat: add URL Encoder / Query String Builder tool

Summary

Add a url-tools.html tool with two tabs: a URL encoder/decoder and a visual query-string builder/parser.

Motivation

URL encoding/decoding is a constant need when debugging API calls, reading logs, or sharing links. Combining it with a query-string builder (key-value table ↔ URL) in one page makes it more useful than a plain encode/decode box and meaningfully differentiates it from simple online converters.

Proposed UX

Tab 1 — Encode / Decode

• Textarea input + output
• Mode toggle: encodeURIComponent (component-safe) vs encodeURI (full-URL-safe)
• Encode and Decode buttons; auto-detects direction on paste if one side is empty
• Copy output button

Tab 2 — Query String Builder

• Parse mode: paste a full URL or query string → decompose into an editable key-value table (rows with key input, value input, enabled toggle, delete button)
• Build mode: add rows → live-assembled URL shown above the table
• Copy full URL and copy query-string-only buttons
• "Add row" button; drag-to-reorder rows

Implementation notes

• Category: Code
• Slug: url-tools
• Icon: 🔗
• No npm dependencies — encodeURIComponent, decodeURIComponent, URL, URLSearchParams, all native
• All logic inline in <script>
• Follow src/_tool-template.html and run bun run generate:sections, bun run generate:index, bun run generate:favicon after adding to tools.json

Start with src/_tool-template.html and tools.json to understand the single-file tool structure and registration flow. Add url-tools.html with the two described tabs and native URL APIs, then run bun run generate:sections, bun run generate:index, and bun run generate:favicon; done means encoding, parsing, building, copying, row editing, and reordering work in the browser.