refactor: replace dotenv with native Node.js process.loadEnvFile

[rahuld109]

Summary

• Replace dotenv.config({ quiet: true }) with native process.loadEnvFile()
• Use try/catch to silently ignore missing .env files
• Remove dotenv dependency from package.json

Closes #636

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.38%. Comparing base (28ee6a9) to head (f1669f2).
⚠️ Report is 293 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (28ee6a9) and HEAD (f1669f2). Click for more details.

HEAD has 3 uploads less than BASE

Flag	BASE (28ee6a9)	HEAD (f1669f2)
	6	3

Additional details and impacted files

@@             Coverage Diff              @@
##            master     #638       +/-   ##
============================================
- Coverage   100.00%   57.38%   -42.62%     
============================================
  Files           15       45       +30     
  Lines          649     3417     +2768     
  Branches         0       15       +15     
============================================
+ Hits           649     1961     +1312     
- Misses           0     1456     +1456     

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