Clean up .env.example (duplicates + alignment with requireEnv())

[robertocarlous]

Title: chore(env): clean up .env.example — remove duplicate JWT block and align with src/config/env.ts

Body:
User story
As a new contributor,
I want .env.example to list each required variable once with correct names,
so that I can copy it to .env and start the server without guessing which JWT_* block is authoritative.

Description
.env.example currently has duplicate JWT_SEED sections and mixed naming. src/config/env.ts uses requireEnv() for several keys; the example file should mirror that contract exactly (placeholders only).
Requirements
Remove duplicate JWT_SEED blocks; keep a single JWT section.
Ensure every requireEnv('...') key from src/config/env.ts appears in .env.example with a clear placeholder (or explicitly marked optional if truly optional).
Align Stellar-related names with the outcome of the “agent secret key” unification issue (same canonical name everywhere).
Quick consistency pass: PORT, NODE_ENV, DATABASE_URL, REDIS_URL, Twilio vars, JWT TTL vars—no contradictions.

Acceptance criteria
[ ] .env.example contains no duplicate keys for the same concept (especially JWT_SEED).
[ ] Variable names match what src/config/env.ts expects at startup.
[ ] A short comment at the top explains: “copy to .env and fill values.”

[Diaroke]

@Diaroke has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

I would love to work on this issue because I can handle it correctly. Kindly assign.

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[D240021]

@D240021 has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Hi! 👋

I’d like to contribute to this issue.

I’m a full-stack developer currently getting started in Web3, and I think this project is a great opportunity to learn while contributing to something meaningful in the ecosystem. I have experience working with backend services, REST APIs, and web applications, and I’m motivated to collaborate and add value wherever possible.

Please let me know if I can take this issue. I’d be happy to work on it 🚀

ℹ️ Repo Maintainers: To accept this application, review their application or assign @D240021 to this issue.

[SudiptaPaul-31]

@SudiptaPaul-31 has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

May I be assigned to this issue I have worked on several open-source projects and also an active open-source contributor and would love to contribute to this issue. I have worked with more than 30+ open-source projects and delivered quality pr's for them which led to faster project delivery

ℹ️ Repo Maintainers: To accept this application, review their application or assign @SudiptaPaul-31 to this issue.

[manoahLinks]

@manoahLinks has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

can i hop on this ?

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[drips-wave]

Congratulations, @SudiptaPaul-31! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on March 30, 2026.

🧑‍💻 @SudiptaPaul-31: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

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