devex: for required env variables.... add easy links to get them

```

> simplegrants.xyz@0.1.0 dev
> next dev

❌ Invalid environment variables: {
STRIPE_SECRET_KEY: [ 'Required' ],
STRIPE_WEBHOOK_SECRET: [ 'Required' ],
STRIPE_WEBHOOK_SECRET_CONNECT: [ 'Required' ],
BLOB_READ_WRITE_TOKEN: [ 'Required' ],
POSTGRES_PRISMA_URL: [ 'Required' ],
POSTGRES_URL_NON_POOLING: [ 'Required' ],
CLERK_SECRET_KEY: [ 'Required' ]
````

for each of these, itd be nice if the .env.example had a link to where i could get a valid env variable. the stripe one is obvious to me.. but th eothers are not. linnk me to the pages/instructions to generate them without thinking?

we should also denote in comments which env variables are required.. for easy setup.

Start by opening .env.example and compare its entries with the missing variables shown in the issue. Add a useful source link for each required variable and comments that clearly mark required values, including setup or generation instructions where needed. Done means a new developer can identify where to obtain every listed value without guessing.

Written by the indexing model from the issue text.