The command palette shows each command's mnemonic, and finds a command by it

[a-team-app]

Context

Second slice of #290: the command palette (Ctrl+E) is the door people reach for first, but it never shows a command's mnemonic, so it can't teach the faster route, and nothing lets you search mnemonics (the mnemonic dialog reads every key as part of a mnemonic). This adds a Mnemonic column to the palette and lets its filter match it. See the palette mockup in the pitch. Independent of the menu bar.

Acceptance criteria

• In the command palette (Ctrl+E, a TextField filter over a ListView), each row shows the label, the keys, and the command's mnemonic as the rightmost column. A command with no mnemonic leaves that column blank.
• The Mnemonic column lines up down the list and stays readable at a narrow terminal width (the label truncates before the mnemonic does).
• Typing sf in the filter lists Save active editor; typing sao lists Select all occurrences (when an editor has focus). Filtering by label or key still works as before.
• Running a row, Esc, and which commands the palette lists where you are are all unchanged.
• Settings › Keyboard Shortcuts and the mnemonic dialog (Ctrl+Space) are unchanged.

Tests

• Rows carry the mnemonic from the one mnemonic table (not a copy), blank when a command has none.
• The filter matches on mnemonic, label and keys; a mnemonic query finds the right command.
• Column layout at a narrow width keeps the mnemonic visible.

Out of scope

• Mnemonics in Settings › Keyboard Shortcuts, or in the menu bar.
• Changing any mnemonic or label, or the palette's scope filtering.
• Ranking results (e.g. an exact mnemonic match first). Filter only.

[a-team-app]

Draft PR #351 is up.