The page is deleted and nothing dangles

[sameera]

As a contributor browsing the delivery-planning space, I want the sequencing page gone rather than narrowed, so that no stale wave table is reachable and the backlog query is the only inventory.

Acceptance Criteria

• Given the repository after this story, when searching tracked files for the path docs/delivery/sequencing.md, then zero matches are returned.
• Given the repository after this story, when searching tracked markdown for a link whose target resolves to the deleted file, then zero matches are returned.
• Given an existing lesson file mentions the page by name in past tense as a historical record, when this story completes, then that mention is left unchanged, because a lesson describes what happened rather than pointing at a live surface.

Notes

This story is blocked by #402 and #403: the page is the source both of them read from, so it is deleted last.

A link check confirmed at planning time that no tracked markdown links to the page; the only textual mentions are past-tense prose in docs/delivery/lessons/. The acceptance criteria assert this rather than assume it, so a link added between planning and implementation is caught.