fix: stop stale refs from silently no-oping and suggest the current ref

[nicobailon]

A ref whose element was re-rendered usually didn't fail. surf click e4 printed OK and did nothing. Surf kept the removed node reachable through window.__piRefs, so the click went to an element no longer on the page. On pages where handlers sit on the document (React), nothing happened. The "not found" error only appeared after garbage collection.

Now a ref works only if its element is still on the page. When it isn't, the error suggests the current element when exactly one visible element has the same role and accessible name:

Element e12 no longer exists. Did you mean e40 (button "Save")? Otherwise run surf read.

With zero or several matches it says to run surf read. It never suggests an element with a different role or name, or one inside an aria-hidden subtree.

• All 11 ref-taking actions use one resolver.
• locate.role, locate.text and locate.label now record the element's real role and name for its ref instead of the search text, so their refs get correct suggestions.
• The accessible-name function moves out of generateAccessibilityTree, and the identical copy in generateYamlTree is deleted, so suggestion names match surf read output. read output is unchanged.
• Guarded semantic click/fill with a ref that doesn't exist returns stale_observation, which the semantic CLI already refreshes and retries.

Refs that survive re-renders are deferred. Checking real sites: keyed React updates (sorting, tabs, react-select, controlled inputs) keep their nodes. A Vue list filter and restore replaced 419 of 499 nodes, and a react.dev page change replaced 583 of 623. Many replaced elements share a role and name: 210 of 419 and only 9 of 208 had a unique match. Carrying refs over automatically would often pick the wrong element. Revisit if the "Did you mean" error shows up often in real agent runs.

Tests: unit tests for a swapped button, different role or name, several matches, unknown refs, locate refs with a partial name, and an aria-hidden container. A real-Chrome e2e case checks the suggestion and that clicking the suggested ref works. Full unit suite, check, lint and real-Chrome e2e pass locally under Node 24.

Closes #340