fix(dialog): prevent cyclic accessibility recursion

[steipete]

Summary

• replace recursive dialog accessibility walks with iterative, identity-aware depth-first traversal
• preserve pre-order, sheet-before-child ordering, and first-match behavior while breaking cycles and deduplicating aliases
• add deterministic coverage for cyclic graphs, shared nodes, first-match short-circuiting, and a 20,000-node hierarchy
• document the fix in the app and CLI changelogs

Test plan

• DEVELOPER_DIR=/Applications/Xcode-beta.app/Contents/Developer swift test --package-path Core/PeekabooAutomationKit --filter DialogElementTraversalTests --no-parallel
• DEVELOPER_DIR=/Applications/Xcode-beta.app/Contents/Developer swift test --package-path Core/PeekabooAutomationKit --no-parallel
• DEVELOPER_DIR=/Applications/Xcode-beta.app/Contents/Developer swiftlint lint --config .swiftlint.yml (13 existing non-serious warnings, none in changed files)
• safe release checks plus swift test --package-path Apps/CLI -Xswiftc -DPEEKABOO_SKIP_AUTOMATION --no-parallel

[clawsweeper]

ClawSweeper status: review started.

I am starting a fresh review of this pull request: fix(dialog): prevent cyclic accessibility recursion This is item 1/1 in the current shard. Shard 0/1.

This placeholder means the worker is alive and reading the current context. I will edit this same comment with the actual review when the claws are done clicking.

Crustacean status: shell secured, claws on keyboard, evidence pebbles being sorted.