Deps: dotenv 18.0.6 and knip 6.40.0 (#102)

## Summary

Dev dependency bumps from the dependency sweep: dotenv 18.0.5 to 18.0.6
and knip 6.39.0 to 6.40.0. Dev only, so this ships nothing to users and
needs no release.

Checked and found current: every exact pin against npm latest. Held
deliberately: eslint stays on 9 (eslint-plugin-import's peer range still
stops at 9) and TypeScript stays on 6 (typescript-eslint's peer still
requires below 6.1), both re-tested today.

Worked with Varun, who asked for the sweep.

## Type of change

- [ ] Bug fix (no breaking change)
- [ ] New feature (no breaking change)
- [ ] Breaking change (existing callers must update)
- [x] Docs, tests, or internal maintenance only

## Public API

Unchanged.

## Test plan

`bun install` re-run to a no-op, then lint, typecheck, knip, test and
build, all green locally.

## Checklist

- [x] Tests cover the new behavior, and the suite passes locally
- [x] Lint, format, and type checks pass
- [x] Docs and README examples updated if the public surface changed
- [x] No secrets, credentials, or personal data in the diff or the tests

Author: vvillait88

bun.lock

@@ -54,11 +54,11 @@
     "@eslint/js": "^9.39.5",
     "@types/node": "^26.6.4",
     "@vitest/coverage-v8": "^5.0.3",
-    "dotenv": "^18.0.5",
+    "dotenv": "^18.0.6",
     "eslint": "^9.39.5",
     "eslint-plugin-import": "^2.32.0",
     "eslint-plugin-unused-imports": "^4.4.1",
-    "knip": "^6.39.0",
+    "knip": "^6.40.0",
     "lefthook": "^2.1.17",
     "tsup": "^8.5.1",
     "typescript": "^6.0.3",