The origins list is keyboard-first: j/k move between rows, enter opens one #10405

One sentence: the origins page joins the shell's j/k row traversal (#3697), the way the map (d621249b4) and flags lists did.

Done:

• [ ] Every row on the origins page that links somewhere carries nav: true in its row({...}); rows with no link and the empty page carry none.
• [ ] test/keys-origins.test.ts (patterned on test/keys-flags-list.test.ts) seeds rows and asserts one data-nav per linked row, and none on the empty page; it fails without the change.
• [ ] bun test test/keys-origins.test.ts passes; bun scripts/design-lint.ts is clean.

Files: src/web/pages/origins.ts, test/keys-origins.test.ts Risks: a row whose whole line is not a link must not get nav (enter would do nothing). No hot file is touched. Crew: a Sonnet builder with the web brief (mason or scout); a person assigns.

Parked by the crew: the check stayed red through 2 automatic tries (pull #10436 closed; its branch scout/10405-the-origins-list-is-keyboard-first-j-k-m at d22c438d926c keeps the work so far). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Parked by the crew: the check stayed red through 2 automatic tries (pull #10492 closed; its branch scout/10405-the-origins-list-is-keyboard-first-j-k-m at 771e444c2481 keeps the work so far).

Parked twice since a person last spoke here, so it is the planner's now. Every reason:

1. the check stayed red through 2 automatic tries (pull #10436 closed; its branch scout/10405-the-origins-list-is-keyboard-first-j-k-m at d22c438d926c keeps the work so far)
2. the check stayed red through 2 automatic tries (pull #10492 closed; its branch scout/10405-the-origins-list-is-keyboard-first-j-k-m at 771e444c2481 keeps the work so far)

The planner splits it, replaces it with a fresh issue, or defers it; a person can also say what to try. Nothing starts here until then, and the board lists it.

Replaced by #10542. Both pulls (#10436, #10492) were red only in the cell suites (spawn-cell-e2e, crew-sandbox #560), which their diff never touched; that is #10541, and #10542 waits for it. #10542 also narrows done to the rows that have a link: only the frozen-mirror rows carry an href, so only they get nav.