Expose aria-pressed/aria-expanded on stateful command buttons

[etuan]

Summary

CommandButton renders active/disabled styling for every command, but never surfaced that state to assistive tech:

• Toggle-style commands (Pan Mode, Pointer Mode) had no aria-pressed, so a screen reader announced them as a plain, stateless button — you couldn't tell whether pan mode was currently on.
• Every menu- or panel-opening command (Document Menu, Page Settings, Zoom Menu, and, once I swept the file for the same shape, the annotation/shapes/form tools overflow menus, the tab overflow menu, and every sidebar panel toggle) had no aria-expanded.

Additionally, "Toggle Pan Mode" / "Toggle Pointer Mode" is an odd accessible name for a button whose pressed state is (now) announced separately — no other toggle in this toolbar says "Toggle" in its name.

Fix

• @embedpdf/plugin-commands: add activeAriaState?: 'pressed' | 'expanded' to Command, resolved onto ResolvedCommand in commands-plugin.ts.
• @embedpdf/snippet:
  • CommandButton maps activeAriaState to the matching ARIA prop (aria-pressed for 'pressed', aria-expanded for 'expanded') and spreads it onto Button.
  • commands.ts: mark pan:toggle/pointer:toggle as 'pressed', and every toggleMenu(...)/toggleSidebar(...)-backed command as 'expanded' (21 commands total — see diff).
  • translations.ts: pan.toggle/pointer.toggle labels changed from "Toggle Pan Mode"/"Toggle Pointer Mode" to "Pan Mode"/"Pointer Mode".
  • mode-select-button.tsx renders its trigger directly rather than through CommandButton, so it gets the same aria-expanded fix applied inline.

Deliberately out of scope

mode:view / mode:annotate / mode:shapes / mode:insert / mode:form are excluded. Their active represents which mutually-exclusive editing mode is currently selected, not a pressed or expanded state — that's a tabs/radiogroup shape (aria-selected/aria-checked on a role="tablist"/role="radiogroup" structure), which is a bigger, separate change I didn't want to fold into this one.

Steps to reproduce (before this fix)

1. Open a document with a screen reader running.
2. Tab to the Pan Mode button and activate it, then Tab back to it (or re-focus). It announces as a plain button with no pressed state, and its name reads "Toggle Pan Mode" rather than "Pan Mode".
3. Tab to the Document Menu / Page Settings / Zoom Menu button and open it. It announces as a plain button with no expanded/collapsed state.

WCAG 4.1.2 (Name, Role, Value).

Changesets

Two changeset files included, one per affected package, per .agents/skills/embedpdf-changesets.

Testing

Manually verified per the repro steps above; no existing test suite for this package.

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