fix(ui): remember call flow host grouping across tabs

[adubovikov]

Summary

• Persists call flow UI preferences in localStorage (homer_callflow_prefs): Host grouping (including Group by alias), Compact, Absolute time, High-contrast Call-IDs.
• Per-call filters (IP/method/payload/call-id exclusions) stay session-local and reset as before.
• Restores Homer 7 behaviour: last chosen grouping survives switching transaction tabs (Messages, QoS, etc.) and reopening the modal.

Test plan

• Open transaction → Call Flow → set Group by alias
• Switch to Messages, then back to Call Flow → grouping still Group by alias
• Close modal, open another call → same grouping remembered
• cd src/ui && npm test -- src/dashboard/flow/flowFilterPrefs.test.ts

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