[AI Assistance] Fail-closed origin locking in network and DOM tools

Network tools (ListNetworkRequests, GetNetworkRequestDetails) previously
checked if an origin lock was established, but fell back to allowing all
requests when conversationOrigin was null or undefined, causing them to
fail open. Similarly, DOM and accessibility tools (GetStyles,
GetElementAccessibilityDetails, ResolveDevtoolsNodePath) relied on
ConversationContext.isOriginAllowed(), which returns true when the
origin lock is not established.

This change migrates all remaining tools to isOriginAllowedByLock and
ensures they fail closed when the origin lock is undefined or opaque:
- ListNetworkRequestsTool and GetNetworkRequestDetailsTool reject
  execution when the origin lock is missing or opaque, and filter
  requests strictly via isOriginAllowedByLock against the initiator origin.
- GetStylesTool, GetElementAccessibilityDetailsTool, and
  ResolveDevtoolsNodePathTool require an established non-opaque origin lock
  and validate target node origins using isOriginAllowedByLock.

Fixed: 559156499
TAG=agy
CONV=401d6ddf-8863-46c0-b0da-516acd8cbdda
Change-Id: I281a52888fd35490ff11e96ac48bcdc6d49a6244
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/8378726
Reviewed-by: Simon Zünd <szuend@chromium.org>
Auto-Submit: Jack Franklin <jacktfranklin@chromium.org>
Commit-Queue: Jack Franklin <jacktfranklin@chromium.org>