[contursofran]

Fixes #744

Steps

1. internal/app/shortcut: Project1..Project8 (⌘⇧1..⌘⇧8) and LastProject (⌘⇧9), with ProjectKeys, ProjectIndex and ProjectShortcut. These use the same numbered-set helper as the tab keys.
2. SpacesList.PickProject selects a project the same way StepProject does (its orchestrator, else its main checkout). windowKeys calls it next to ⌘⌥←/→.
3. Project row key chips: "⇧1".."⇧8", and "⇧9" on the last row when it is past the eighth.
4. Docs: KeyHints.md, ProjectRow.md, the shortcut table in spec README, and D289.

Notes

• MyGo matches the physical key with exact modifiers (darwin keycode 0x12 → Key1). So ⌘⇧1 arrives as Key1 with ⌘⇧, not "!", and does not fire ⌘1. No menu item, terminal key or composer key uses ⌘⇧digit.
• A row shows only one chip. The rows before and after the open project keep ⌥←/⌥→, because existing tests (Key hints: place each chip on its element's icon; shortcut to jump between projects #645, D248) expect them. The other rows show ⇧N. This needs a decision from the owner.
• No Settings or help view lists shortcuts.

Pre-check

1. Tests: TestCmdShiftNumbersSelectTheProjectsOfTheSidebar (handler undone), TestTheOtherProjectRowsShowTheirNumberChips (hint undone), TestProjectKeysAndProjectIndexAgree and TestCmdShiftNumbersPickTheProjects (index undone): each one failed with its change undone.
2. Plan: all steps done. One deviation: the chips on the rows before and after the open project (see Notes).
3. Contract: ids project-1..8 and last-project; chips ⇧1..⇧9.
4. Up to date: merged origin/main.
5. Diff read: no leftovers.
6. Coverage: all acceptance lines of the issue are done. Exception: rows next to the open project show ⌥←/⌥→, not ⇧N.
7. Duties: nothing removed. The tab helpers now delegate to the shared numbered set.
8. Evidence: scripts/see.sh multi dark with chips shows "⇧1" on demo.