feat(text): 'get text --pierce' reads through CLOSED shadow DOM (#30)

Some injected UI (browser-extension debug panels, web components) renders into a
CLOSED shadow root that eval/innerText cannot read. --pierce walks the CDP DOM
tree (DOM.getDocument depth:-1 pierce:true), which includes closed shadow roots
and child documents, and collects text nodes (skipping script/style/etc).

Review-safe: rides the per-tab debugger session already attached, no new Chrome
permission and no ab-connect/extension change — so it works in extension-relay
mode without touching the published extension. Verified live: a closed-shadow
panel that main-world eval reports HIDDEN is read in full via --pierce.

First slice of #30 (read extension/injected-panel content). Deeper extension
introspection (background SW / chrome.storage) stays a launch-mode / raw-CDP
concern, deliberately NOT done by expanding ab-connect's debugger powers.

skill-data/core/SKILL.md

@@ -210,6 +210,7 @@ For unstructured reading (no refs needed):
 chrome-use get text                    # WHOLE PAGE — all frames by default (see below)
 chrome-use get text @e1                # visible text of one element (or a CSS selector)
 chrome-use get text --main             # main content only — skip nav/header/sidebar
+chrome-use get text --pierce           # read through CLOSED shadow DOM (injected panels)
 chrome-use frames                      # list every frame + where the text lives
 chrome-use get html @e1                # innerHTML
 chrome-use get attr @e1 href           # any attribute
@@ -234,6 +235,12 @@ holds what), run `chrome-use frames`. To **cut boilerplate** (global nav/header/
 footer, "related items" sidebars), use `chrome-use get text --main`. If content
 is lazy-loaded, `scroll` it into view first, then read.
 
+**Closed shadow DOM.** Some injected UI (browser-extension debug panels, web
+components) renders into a *closed* shadow root that `eval`/`innerText` cannot
+read. `chrome-use get text --pierce` reads through closed shadow roots and child
+documents via the CDP DOM tree — use it when content is clearly on screen (you
+see it in a screenshot) but `get text`/`eval` come back empty.
+
 ## Interacting
 
 ```bash