Add previous thread links to weekly standups

[Mshehu5]

This PR address https://github.com/orgs/payjoin/discussions/1451#discussioncomment-16395855

Link each contributor's new weekly standup thread to the corresponding thread from the prior check-in discussion.

Notes for reviewers:
I tried a version that parsed each contributor’s replies and copied parts of that text into the next automated standup thread. I’m not proposing that here Per Dan’s point that process changes should be small and easy to review this felt too complex for a first step.

Better if changes to the process can be small, easy to review, and independent so that we can just get some subset of them merged ASAP, hopefully for next week.

That approach depends on contributors using headings like "Focus" consistently. It also gets awkward if someone posts multiple replies in a thread or if part of the useful context comes from follow up discussion with Dan rather than from the contributor’s own structured reply. In those cases the bot can easily carry forward the wrong thing or drop important context entirely.

This change is a narrower first step that still addresses the accountability concern by linking each contributor’s new thread to their previous one. It is probably not the final design but it is a simpler and safer starting point.

P.S if you have input on a preffered followup PR please drop them here

Pull Request Checklist

Please confirm the following before requesting review:

• I have disclosed my use of
  AI
  in the body of this PR.
• I have read CONTRIBUTING.md and rebased my branch to produce hygienic commits.

[coveralls]

Pull Request Test Coverage Report for Build 23948167383

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 84.34%

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Totals
Change from base Build 23927050434:	0.0%
Covered Lines:	10798
Relevant Lines:	12803

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💛 - Coveralls

[Mshehu5]

test run in :
https://github.com/Mshehu5/rust-payjoin/actions/runs/23948953071/job/69851514684

click -> Run python .github/scripts/create_standup_discussion.py in the action to see results

cc @arminsabouri @DanGould

would appreciate your review