fix(cua-driver): preserve snapshot-owned screenshot transforms - #3942

Refs #3630

Problem

A later screenshot can replace the coordinate transform used by an earlier
observation. A client can then send a valid pixel coordinate that Driver
silently interprets in another capture's scale.

Change

• Publish screenshot scale and zoom interpretation data with the authoritative
  runtime-owned snapshot.
• Resolve coordinate actions against the calling session's current snapshot and
  refuse stale, cross-session, ambiguous, or retired context.
• Retire screenshot and zoom context on replacement, explicit removal,
  session end, eviction, and late-completion races.
• Bound retired-snapshot tombstones and fail closed after overflow until the
  cache is cleared.
• Preserve coordinate-less button release using the stored native hold point.
• Convert persistent Wayland press and drag coordinates from window-local to
  compositor output space.
• Release session-owned persistent Wayland holds through the fallible cleanup
  hook, retaining failed releases for bounded retry.
• Add focused shared and platform harness regressions for cross-client
  replacement, independent windows, stale zoom, late completion, and
  Windows native-coordinate dispatch.

This preserves the current public action shapes and latest-read replacement
behavior. It does not add historical screenshot IDs or the future perception
capture registry.

Attribution

Salvaged from #3628. The initial implementation commit preserves
Co-authored-by: injaneity <[email protected]>.

Validation

Current head: de0e5ff5c634baf63f5ac9e913e5de6f77a4e094

• cargo test -p cua-driver-core element_cache::tests --lib: 27 passed
• cargo test -p platform-linux --lib: 23 host-platform tests passed
• cargo check --workspace: passed with existing warnings
• cargo fmt --all -- --check: passed
• git diff --check origin/main...HEAD: passed
• cua-driver-platform.test.ts: 6 passed
• Generator routing assertions: passed
• Native Linux/Windows zoom references independently reviewed against their Rust contracts: no findings
• Exact-head Linux Rust: run 35242959146 passed
• Exact-head Windows Rust: run 35242959092 passed
• Exact-head native references: run 35242959101 passed on macOS, Linux, and Windows
• Exact-head contract/SDK: run 35242959283 passed
• Exact-head Nix: run 35242959129 passed
• Independent final diff review: no findings

Remaining draft gates

• The repository-wide CI: Test Scripts / test job still carries the inherited
  CI: release-wiring test rejects deduplicated AGENTS guidance #3935 release-guidance regression; this PR does not change the affected files.
• Canonical macOS, Windows, and Linux desktop E2E on the exact stable candidate
  before this PR is made ready or merged.

This PR remains draft and unmerged.