[Feat]: Cmd+Shift+O (Open markdown tab) does nothing in the main window — only works in Floating Terminal

Operating system: macOS
Orca version: v1.4.137

Details:

Short summary:
The "Open markdown tab" command (`tab.openMarkdown`, default `Cmd+Shift+O`) has no effect when focus is in the main window. It only works inside the Floating Terminal panel (`Cmd+Alt+A`). "New markdown tab" (`Cmd+Shift+M`) works fine in the main window, so the two behave inconsistently even though both appear the same in Settings → Shortcuts.

What happened?
Pressing `Cmd+Shift+O` in a normal worktree does nothing — no file picker, no tab. The same shortcut works only when the Floating Terminal panel is focused.

How can we reproduce it?
1. Open Orca on a normal worktree (main window, not the floating terminal).
2. Press `Cmd+Shift+O`.
3. Nothing happens (no native "Open markdown" file picker, no new tab).
4. Open the Floating Terminal (`Cmd+Alt+A`), focus it, and press `Cmd+Shift+O`.
5. The native "Open markdown" file picker now appears as expected.

Expected:
`Cmd+Shift+O` should open the markdown file picker in the main window too — consistent with `Cmd+Shift+M` (New markdown), which does work in the main window. (Alternatively, if it is intentionally floating-only, it probably shouldn't be presented as a general shortcut in Settings.)

Likely root cause (from inspecting the packaged app.asar, v1.4.137 — line up against the TS source):
- `tab.openMarkdown` appears to be wired only through `FLOATING_WORKSPACE_PANEL_SHORTCUT_ACTIONS`, so it fires only when the key event target is inside the floating panel.
- The main-process `before-input-event` handler dispatches `tab.newMarkdown` → `ui:newMarkdownTab`, `tab.newTerminal` → `ui:newTerminalTab`, `tab.newBrowser` → `ui:newBrowserTab`, etc., but has **no branch for `tab.openMarkdown`** (there is no `ui:openMarkdownTab`).
- The renderer exposes an `onNewMarkdownTab` IPC listener but no `onOpenMarkdownTab`, and the renderer's central keydown handler has no markdown `matchShortcut`.
- Net effect: in the main window the `Cmd+Shift+O` keystroke is never routed to an "open markdown" action.

Workaround:
Use `Cmd+P` (Go to File) to open a markdown file, or open it from the Floating Terminal panel.