chore(ci): add stale issue triage workflow

[EliteCoder18]

Description

Part of #410
Closes #386

Adds .github/workflows/stale.yml using actions/stale@v10 to automatically label and close inactive issues and abandoned PRs.

• Issues inactive for 180 days → stale label → closed after 30 more days
• PRs inactive for 180 days → stale label → closed after 30 more days
• Exempt: labels release,security,audit,do-not-close,good first issue for issues and blocked,security,do-not-close for PR
• Runs weekly on Mondays at 09:00 UTC
• PR trigger forces dry-run mode automatically for safe CI validation

Notes to the reviewers

• Recommend a workflow_dispatch dry run with debug_only=true right after merge to preview impact before the Monday cron fires
• do-not-close and blocked exemption labels don't exist in the repo yet, create them before merging if you want manual override capability

Changelog notice

ci: Automated stale issue and PR triage workflow

Before submitting

• I followed the contribution guidelines
• This PR breaks the existing API

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.96%. Comparing base (d8e006f) to head (d466b08).
⚠️ Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #497      +/-   ##
==========================================
+ Coverage   80.93%   80.96%   +0.02%     
==========================================
  Files          24       24              
  Lines        5482     5489       +7     
  Branches      247      247              
==========================================
+ Hits         4437     4444       +7     
  Misses        968      968              
  Partials       77       77              

Flag	Coverage Δ
rust	80.96% <ø> (+0.02%)	⬆️

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[notmandatory]

Concept ACK.

We'll discuss with the team at our next call to confirm the time frames for making something stale make sense to everyone.

[notmandatory]

Suggested change

	This issue has been inactive for 180 days and labeled **stale** Comment to keep it open. It will be closed in 30 days if there is no activity.
	This issue has been inactive for 180 days and labeled **stale**, comment to keep it open. It will be closed in 30 days if there is no activity.

[EliteCoder18]

Updated in the latest rebase, thanks.

[Dmenec]

Concept ACK. Just a little nit on close reason.

[Dmenec]

not_planned fits an inactivity close better (as mentioned in actions/stale#789), and since it's the default option we could just drop the line.

[EliteCoder18]

Good point, updated.

[ValuedMammal]

I would be generous and leave PRs open for 180 days. Suggest removing discussion from exempt labels. If there are long running discussions, they can happen in https://github.com/bitcoindevkit/bdk_wallet/discussions

[EliteCoder18]

I would be generous and leave PRs open for 180 days. Suggest removing discussion from exempt labels. If there are long running discussions, they can happen in https://github.com/bitcoindevkit/bdk_wallet/discussions

@ValuedMammal Thanks, updated the exempt labels. I also adjusted the PR timeout to 180 days.

[ValuedMammal]

I would be generous and leave PRs open for 180 days. Suggest removing discussion from exempt labels. If there are long running discussions, they can happen in https://github.com/bitcoindevkit/bdk_wallet/discussions

@ValuedMammal Thanks, updated the exempt labels. I also adjusted the PR timeout to 180 days.

Can we update the {stale|close}-pr-message to reflect the 180/210 days of inactivity as well.

[EliteCoder18]

Updated the workflow based on the Lib Standup discussion:

• Pinned actions/stale to a commit hash for improved security.
• Simplified the PR close message.
• Fixed indentation and removed unnecessary blank lines.

[notmandatory]

ACK d466b08

Great first step in helping close old issues and PRs in this repo. If all goes well I'd like to see this workflow in other repos in the org.