Memoize Playwright page target IDs

[ehfeng]

Summary

• cache successful Playwright page-to-CDP target ID lookups in a WeakMap
• coalesce concurrent discovery and prevent pre-reset work from repopulating the cache
• refresh cached IDs on the resolver retry and reset them on browser disconnect
• build a per-attempt pageByTargetId index for the tab-to-page join
• add focused Node tests for reuse, refresh, failures, concurrency, and reset behavior

Scope

This PR intentionally leaves browser-level CDP session consolidation unchanged. It isolates target-ID memoization and stale-cache recovery from that separate lifecycle refactor.

Stack

• based on Allow page-free Playwright execution to skip active-tab resolution #352
• Allow page-free Playwright execution to skip active-tab resolution #352 is based on Handle Playwright active tabs across contexts #347

Validation

• make test-runtime
• go test ./e2e -run ^$
• go vet ./...
• go test -race ./cmd/api/api ./lib/oapi
• Playwright daemon bundle build

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Note

Medium Risk
Changes which Playwright page the daemon binds for user code (foreground tab resolution) and adds caching that must stay correct across CDP reconnects and target replacement.

Overview
Adds PageTargetIdCache to memoize CDP targetId lookups per Playwright Page (WeakMap keys, shared in-flight discovery, optional refresh, and reset on browser disconnect/reconnect). Active-tab resolution now builds a pageByTargetId index from the cache instead of opening a CDP session per page on every join, and pageForTabTarget matches related targets via that map.

resolveActivePage uses one browser CDP session per attempt, refreshes cached IDs on retries, bumps attempts to 3 with a 150ms delay between passes (for cross-origin tab target swaps), and logs unmatched active tab IDs on fallback.

CI/build: make test-runtime runs Node tests for the cache; server unit workflow adds Node 22 and runs it; headful/headless Dockerfiles bundle the new module into the Playwright daemon esbuild step.

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[rgarcia]

superseded by #356 — same memoization work rebased directly onto #347 (the resolve_active_page middle PR was dropped from the stack, see #352), plus browser-level CDP session consolidation. GitHub's stack metadata blocked retargeting this PR's base, so it was recreated.