docs: align plan-window and pipeline documentation

[id774]

Summary

• Remove the remaining current-provider plan assumptions from comments, docstrings, tests, and operations documentation.
• Describe publication windows and pipeline dependencies through configured semantics rather than mutable provider terms or fragile step counts.
• Correct the data-source error description to match the existing error categories.

Validation

• git diff --check
• POSIX shell syntax check for run.sh
• Ruff
• default pytest suite with integration tests excluded

Scope

• Documentation, comments, error wording, and test-only naming cleanup only.
• No runtime behavior, dependency, version, data-contract, or release-history change.