fix: skip missing seed env files

[sourishkrout]

Summary

• treat seed EnvFiles as optional ordered candidates
• skip missing dotenv files while preserving read/parse errors
• expand implicit seed env-file defaults to .env, .env.local, .env.development, .env.dev
• cover internal seed, raw value store, and public pkg/owl/seed behavior

Verification

• go test ./internal/seed ./pkg/owl/seed -run 'Test(NewStore|NewRawValueStore|DotenvVariables)' -count=1 -v
• make check
• runme run test
• runme run lint