Name a report input's belief time prior, as report parameters already do #2820

Report parameters name their belief time prior since v1.1.0 (#2551), as schedule and forecast parameters do, with belief_time still accepted. The input entries of a report config kept belief_time (flexmeasures/data/schemas/io.py, the Input schema).

An input's belief_time selects the beliefs known at that time, which is what prior means elsewhere. It kept its old name only because the Input schema mirrors TimedBelief.search's keywords, not by design.

Proposal:

• Name it prior in the Input schema, and keep accepting belief_time as a legacy alias, as Time every automation run the same way: offsets and a duration, and no fixed moments #2551 does for report parameters.
• Update the reporting docs and examples, and add a changelog entry.
• Leave beliefs_after alone (see fix: let annotation searches filter by belief time #2367, which found no established replacement name).

Raised in the review of #2818: #2818 (comment)

🤖 Generated with Claude Code

https://claude.ai/code/session_01UBBvKZkzbfEPKctwTN8SDf