feat: rethink planned operation expiration logic

[corentin-core]

Context

Currently, planned operations outside the 5-day tolerance window are silently advanced to the next period. This means a missed operation disappears from the forecast without any user awareness or action.

The current behavior:

• Within 5 days of balance date: "late" (postponed to tomorrow)
• Beyond 5 days: silently advanced to next period (effectively ignored)

Proposed solution

• Rethink the expiration logic: don't silently ignore missed operations
• Consider a more tolerant window (e.g. 1+ month) or a dedicated "pending user action" state
• Define a clear state machine for operation lifecycle (pending → late → expired/cancelled)
• Determine what happens if the user never acts (eventual automatic expiration?)

Acceptance criteria

• Missed planned operations are not silently skipped
• Clear expiration policy defined and implemented
• Edge cases handled (recurring vs one-time, multiple missed iterations)

Related issues

• Related to feat: alert user about late planned operations with action options #204 (user alert/action for late operations - the UI counterpart)