fix: migrate Deno standard library imports to JSR (#455)

[Manish-Dark]

Description

Closes #455

This PR migrates all Deno standard library dependency imports from https://deno.land/std to JSR (@std/*) specifiers in deno.json, resolving Deno 2 lint errors (no-import-prefix) regarding inline dependency URLs.

Summary of Changes

• JSR Migration: Added @std/dotenv, @std/http, @std/assert, and @std/testing under imports in deno.json.
• Import Specifiers Refactoring:
  • main.ts: Replaced https://deno.land/std@0.224.0/http/server.ts with @std/http/server.
  • deps.ts: Updated assertion and mock imports to @std/assert and @std/testing/mock. Replaced inline https:// URLs for soxa and redis with mapped specifiers.
  • render_svg.ts: Replaced https://deno.land/x/dotenv@v0.5.0/load.ts with @std/dotenv/load.
• Type Safety Improvements: Refactored render_svg.ts to replace any assertions with strict instanceof ServiceError type narrowing.
• IDE & Development: Added deno.d.ts ambient declarations and workspace settings for IDE support.

Validation & Testing

• ✅ Linter: deno lint passed with 0 errors across 34 files.
• ✅ Formatter: deno fmt applied across all codebase files.
• ✅ Test Suite: deno task test passed all 10 unit tests.
• ✅ SVG Output: Verified local SVG rendering via render_svg.ts and local server execution (main.ts).