Documentation: add ADR-005 for fee-bump transaction design

[Ejirowebfi]

Description

Fee-bump transactions are documented in README.md but there is no Architecture Decision Record explaining why this approach was chosen over alternatives (e.g., sponsored reserves, pre-funded accounts).

Tasks

• Create docs/adr/ADR-005-fee-bump-transactions.md
• Document the problem, considered alternatives, and decision rationale
• Link the new ADR from README.md
• Follow the format of existing ADRs in docs/adr/

Acceptance Criteria

• ADR file exists at the correct path
• It covers: context, decision, alternatives considered, consequences
• README.md links to the new ADR

[YfengJ]

Hi, I'd like to apply for this if it is still available. I see the previous PR for this scope is closed, so I would wait for assignment/maintainer confirmation first, then add docs/adr/ADR-005-fee-bump-transactions.md following the existing ADR format, cover context/decision/alternatives/consequences, and link it from the README. I won’t open a PR unless assigned or explicitly confirmed.

[milah-247]

I'm interested in contributing to this issue. I have experience analyzing codebases, implementing fixes, and writing comprehensive tests. I'll ensure the solution aligns with project standards and submit a clean PR for review.

[milah-247]

I'm interested in contributing to this issue. I have experience analyzing codebases, implementing fixes, and writing comprehensive tests. I'll ensure the solution aligns with project standards and submit a clean PR for review.

[grantfox-oss]

🦊 GrantFox — @milah-247 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #758)
2. Your PR will be reviewed by the Favourorg maintainers

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