A menu bar across the top lets me browse and run every command by subject

[a-team-app]

Context

First slice of #290: a menu bar across the top of the window, so you can browse everything TuiCode can do by subject (File, Edit, Selection, View, Go, Diff, Review, Help) and reach it with the keyboard or the mouse, without knowing a command's name first. The pitch has the mockups and the full command-to-menu mapping (Where every command lands, plus Git blame at the foot of Diff per Decided #8).

Acceptance criteria

• A one-row menu bar runs the full width of the window, above both the sidebar and the editor, reading File Edit Selection View Go Diff Review Help. It's always there, including with no folder or file open.
• The bar and its menus use the active theme's menu colours, and follow a theme switch in Settings.
• F10 opens the File menu. ←/→ move between menus, ↑/↓ walk items, Enter runs the item, Esc closes the menu and puts focus back where it was.
• F10 is listed as Show menu in Settings › Keyboard Shortcuts and can be rebound there like any other command.
• Where the terminal delivers Alt+<letter>, Alt+F, Alt+E, Alt+S, Alt+V, Alt+G, Alt+D, Alt+R and Alt+H open their menus. Where it doesn't, F10 still works.
• Clicking a menu title opens it; clicking an item runs it; clicking outside closes it.
• Every command that has a mnemonic appears in exactly one menu, in the menu and order the pitch's mapping gives, with separators where it draws them. Show all commands and Show mnemonics are under Help.
• Go › Focus editor tab ► opens a submenu of tabs 1 to 9.
• Each item shows its label and, right-aligned, its current key (the way the palette shows keys, e.g. Alt+↓); an item with no key shows only its label. No item shows a mnemonic. After rebinding a command in Settings, its menu item shows the new key.
• Running an item acts on what you were on before you opened the menu: e.g. with focus in an editor, Edit › Move line down moves that editor's line; with focus in a diff tab, Diff › Next change moves to the next change in that diff.
• An item picked where its command doesn't apply behaves as that command's key would there (the same status message, or nothing), and doesn't crash.
• Every item is listed whatever the context in this slice — dimming comes in a later task.

Tests

• The mapping: every command with a mnemonic appears in exactly one menu, and every menu item names a registered command. A new command with a mnemonic and no menu home fails the test.
• Menu hot-key letters are unique across the eight menus.
• An item runs its command once, by id, through the same path as the palette (not a second key binding that would fire twice).
• The item's key column follows the live bindings, including after a rebind and for an unbound command.
• A command run from the menu acts in the scope captured when the menu opened (an Editor-scoped and a Diff-scoped case).
• F10 opens the menu by default and is rebindable; the bar is laid out above the sidebar and editor without shifting what they show.
• Update AGENTS.md: adding a command means giving it a menu home. Add to the TUI style guide that a menu bar is how the app exposes its commands.

Out of scope

• Mnemonics in the menus, or any change to mnemonics or command labels.
• Dimming or hiding items that don't apply here (a later task).
• The command palette's Mnemonic column (a separate task).
• A setting to hide the menu bar, context menus on right-click, toolbars.
• Any new command other than Show menu, or any change to what an existing command does.

[a-team-app]

Draft PR #350 is up.

[jamescrosswell]

It's a little hard to distinguish the menu from the explorer pane. We should make it visually distinct.

We've already done this in the a-team repo so look at how it's done there (colours used for each theme etc).

[jamescrosswell]

Lots of commands are showing as available even though they're not relevant.

For example the Edit menu shows all the commands to move lines up/down and change grammar even when I don't have an editor open.

We already went through the process of describing which commands should be available in which scenarios to filter the list of available commands in the command palette and mnemonics dialogs. That same rationale/logic should apply to the menus.

[a-team-app]

Done in 7990422 on #350. The menu bar now uses the a-team dashboard's Menu colours in every theme: blue #2B5A8A with yellow hotkeys in Midnight and Daylight, and hotkeys underlined in all four themes. One difference from a-team: Modern Borland's bar there is the same cyan as our explorer, so here it's grey #A8A8A8 with red hotkeys. A test now checks that the bar's background differs from the explorer's in every theme.

[a-team-app]

Done in 4baf895: menu items now use the palette's rule (Global or the scope the menu opened from, and enabled). Items that fail it are greyed out and skipped by the arrows, rather than hidden, so the menus keep their shape and Selection/Diff never open empty. If you'd rather they disappear like in the palette, say so and I'll switch.

[jamescrosswell]

If all of the items in a particular top level menu are unavailable, we should hide and collapse that menu (no point in showing it).

For example if I have no file open:

[a-team-app]

Done in 19a9d2f on #350: a menu with nothing that can run where you are now leaves the bar, and the rest close up (e.g. Selection and Diff with no file open). It comes back once one of its commands can run. Alt+letter and the arrows skip it while it's gone.

[jamescrosswell]

• I think we should remove Focus sidebar, Focus editor, Focus editor tab strip and Focus editor tab from the menu - they're a bit confusing there since the act of selecting the menu itself shifts focus.
• In the View menu, move Toggle sidebar so that it's grouped with the Widen/Narrow sidebar commands
• VS Code's View menu has all of the various side panels as options there (Explorer, Find Review in our case). We should do the same - this means moving Focus review to the View menu. I think we could rename them all at that point to just Explorer, Find and Review as the fact that they're under the View menu makes it implicit we want to view these...
• We could put a separator between the Open settings item and the Quit item on the File menu

[a-team-app]

All four done in #350:

• Focus sidebar/editor/tab strip/tab N are off the menu (still in the palette and mnemonics).
• View now opens with Explorer, Find, Review (Find moved from Edit, Review from the Review menu), then Toggle/Widen/Narrow sidebar together.
• File has a separator before Quit.