97d426ec6562e61f2cac3aef1869f863ff18a0b3  sidePanel API is missing features from newer Chrome versions

Classified as not security-relevant.
Triage note: Implements new sidePanel.getLayout()/close() WebExtension APIs plus a getTabFromIdentifiers() helper refactor of existing tab-resolution logic. Pure feature work and plumbing; no memory-safety or logic bug fixed.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+6.47), null_guard (+2.59), uaf_lifetime (+4.75), large_churn (-2.0)