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>

skills/agent-browser/SKILL.md

@@ -64,6 +64,8 @@ agent-browser type @e2 "text"         # Type without clearing
 agent-browser select @e1 "option"     # Select dropdown option
 agent-browser check @e1               # Check checkbox
 agent-browser press Enter             # Press key
+agent-browser keyboard type "text"    # Type at current focus (no selector)
+agent-browser keyboard inserttext "text"  # Insert without key events
 agent-browser scroll down 500         # Scroll page
 
 # Get information