[DerekMarshall]

Closes #679. The list's pages are now counted from the top, so a jump always shows the page holding the cursor, and l off a page's last column opens the next page at its first column.

The bug

The settle snapped view_top to a multiple of the page size it had just measured. A page holds as many columns as fit, and a column is as wide as its longest name, so neighbouring pages differ in length. The settle alternated between two starts and kept the lower one. After a / search no row was lit, and l landed in the next page's second column.

The fix

• Fixed pages (ui::list_view::Pages): the first page starts at row 0 and each starts where the one before it ends. The starts are found by walking from the top, once per listing and list size, and only as far as asked. settle_page replaces stabilize_grid's loop and places the column on the page holding its cursor.
• PageDown / PageUp move to the same column and row on the next or previous page, or to its last row when it's shorter. PageDown from the last page wraps to the first. PageUp from the first page goes to the last row, so opening a directory measures only its first two pages.
• grid_at is now the one geometry the renderer, the hit-test and the page walk share. Commander::ensure_cursor_visible and cursor_move_global are gone, and ARCHITECTURE.md records the decision.

Checks

• test(list): red cases for a page that hides the cursor after a jump #680's red cases now pass, with their ignores removed. Two more key-driven cases cover PageDown to a narrower page and PageUp to the previous page's first row. All four failed on the old code.
• Unit tests cover the page walk: pages from the top and their wrap, a row's page not depending on earlier lookups, re-measuring on new rows or size, and the first page measuring only two pages. Each was bite-checked.
• A temporary sweep, not committed because it takes over two minutes, covered every row of the 600-name fixture at 238×60 and with a 16-row list. It ran a jump, l, h, PageDown and PageUp, and the cursor bar was on the cursor's name every time.
• In a release build, reaching row 99,999 of a 100k-entry listing takes 3.5 ms once after each listing change; after that a lookup takes 17 ns.
• make check-ci passes. The owner tested a build and approved it.

Generated with Claude Code