feat(account-tree-controller): always fire :selectedAccountGroupChange on init

[ccharly]

Explanation

We used to not persist the selectedAccountGroup property before this change:

• fix: move selectedAccountGroup to top-level persisted state #8245

As a side-effect of this new persistence, we're not re-sending :selectedAccountGroupChange on init and a lot of controllers were relying on this behavior.

We re-introduce this behavior so every controllers can decide how to handle that.

References

N/A

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Medium Risk
Changes event-emission semantics so selectedAccountGroupChange now fires on every init/reinit, which may trigger extra startup work or duplicate handling in subscribers that assumed it only emitted on changes.

Overview
Ensures AccountTreeController always publishes AccountTreeController:selectedAccountGroupChange at the end of init (and therefore reinit), even when the selected group value is unchanged.

Adds a regression test covering the reinit-with-same-accounts case and updates the package changelog to document the restored behavior.

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