feat: add keyboard command for raw keyboard input (#521)

Adds `keyboard type` and `keyboard insertText` subcommands that
operate on the currently focused element without requiring a selector.

Essential for contenteditable editors (Lexical, ProseMirror, CodeMirror,
Monaco) where `type <selector>` doesn't trigger the editor's internal
event pipeline (beforeinput/DOM mutation).

- `keyboard type <text>` — page.keyboard.type() with real keystrokes
- `keyboard insertText <text>` — page.keyboard.insertText()

Note: `keyboard press` intentionally omitted — the existing top-level
`press` command already operates on current focus.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

docs/src/app/commands/page.mdx

@@ -13,6 +13,8 @@ agent-browser dblclick <sel>          # Double-click
 agent-browser fill <sel> <text>       # Clear and fill
 agent-browser type <sel> <text>       # Type into element
 agent-browser press <key>             # Press key (Enter, Tab, Control+a) (alias: key)
+agent-browser keyboard type <text>    # Type at current focus (no selector needed)
+agent-browser keyboard inserttext <text>  # Insert text without key events
 agent-browser keydown <key>           # Hold key down
 agent-browser keyup <key>             # Release key
 agent-browser hover <sel>             # Hover element