Abandon recurring occurrences superseded by their next iteration

A weekly task not done before the next one lands is stale, not still
owed. The scheduler already created the successor regardless of
completion (deliberately, so skipping one doesn't stall the series), but
nothing retired the occurrence it replaced -- so every skipped occurrence
stayed open forever as a permanent overdue item. Live: "Bills" and
"Bones's meds" each sat in the list twice.

AdvanceDueRecurringTasks now marks the superseded occurrence abandoned
when it creates the successor. A separate flag rather than `completed`,
because these were never done and crediting them would corrupt
completion history. All four open-task queries filter it out; migration
030 adds the column and backfills the occurrences already superseded
(exactly the 2 above, verified against production before deploying).

Supersedes the earlier view-level collapse (10f9fcd, reverted in
96518ad): that kept the *earliest* open instance, which is backwards --
the stale one should go and the current one stand -- and it only hid the
row in the flat list while leaving it overdue in the timeline and widget,
which is where it was actually being seen.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018AwnALZL6bD4VBtATDVv3B

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