refactor(ios): prune converged snapshot paths and close release gates

[thymikee]

Parent: #2188

Blocked by: #2195, #2198

Outcome

Delete the compatibility and backend-name policy that remains solely for the migrated iOS snapshot
implementation, enforce no-regrowth at the owning seams, and run the final package-size,
conformance, provider, Simulator, proxy, and affected release evidence.

This is a deletion and enforcement issue, not a place to finish incomplete behavior from blockers.
Each owning migration must already have removed its obvious local duplication; this issue audits and
closes the cross-cutting remainder.

Prune audit

Delete when equivalent engine-interface coverage is already proven:

• shouldPresentIosInteractiveSnapshot from src/core/snapshot-state.ts;
• backendScopesAfterWire and remaining backend-name scope planning;
• direct presentIosInteractiveSnapshot orchestration from buildSnapshotState;
• remaining provider-specific post-wire scope/option branches;
• remaining synthesized WebDriver hittability;
• old iOS semantic-compaction locations after capture-kit owns the implementation;
• runner-local Swift geometric-presentation copies after the runner and harness use the shared source;
• simulator observation dependencies on runner readiness and repeated bridge retries after the
  generation circuit opens;
• tests whose only purpose was to assert removed producer-name branches, after equivalent behavior is
  covered through the engine interface.

Move matching path-keyed fallow baselines rather than regenerating unrelated baselines. Stage new
structural modules before trusting the layering scan.

Do not delete

• XCTest tree, query-sweep, or private-AX capture backends.
• Apple runner manager/cache, .xctestrun preparation, or interaction protocol.
• Swift geometric presentation or TypeScript iOS semantic compaction.
• Generic scope/normalization, refs, quality, occlusion, Android policy, provider acquisition
  adapters, golden fixtures, fuzz harnesses, live smokes, or physical-device code.
• Proxy routes, device leases, authentication, artifact transfer, or RPC compatibility machinery.

If deletion appears possible only by weakening another consumer, stop and report the remaining owner
rather than adding a compatibility re-export or fallback.

No-regrowth enforcement

• Add or update structural ownership tests so producer adapters cannot import presentation behavior,
  contracts cannot own algorithms, and root orchestration cannot reconstruct engine policy.
• Reject old path recreation, backend-name scope/presentation branching, or direct iOS presenter
  invocation outside the engine.
• Plant each new forbidden direction/path and record the named red failure before returning green.
• Do not add allowlists for unclassified paths; fix the declaration or ownership seam.

Final evidence

• Compare packed, clean-installed, and bundled npm sizes with test(ios): establish snapshot convergence baselines and permanent evidence #2189. Report exact deltas; do not use
  source-line estimates. The compiled bridge cache remains outside the npm artifact.
• Run the independent Swift/TypeScript golden corpus, bounded differential fuzz, properties, and
  structural gate with reproducible artifacts.
• Run Appium and Limrun provider contracts on the exact head.
• Run local Simulator cold-cold, cold, warm, relaunch, bridge crash/timeout/cancellation, stale
  generation, fallback, and first-runner-interaction evidence.
• Run direct/proxy semantic parity, controlled-RTT performance, lease isolation/expiry, cancellation,
  and supported version-skew evidence.
• Run pnpm check:affected --run; GitHub remains authoritative for native, provider, coverage, and
  full macOS/Simulator lanes.
• Update CLI help/user docs only if observable behavior changed. Do not document internal producer
  selection. Keep physical-iPhone behavior explicitly unchanged and separately owned.

Acceptance

• No compatibility surface remains solely for the migrated implementation.
• Old paths and forbidden dependency directions have observed planted-red no-regrowth proof.
• All child acceptance evidence is linked from iOS snapshot backend convergence and fast Simulator observation #2188 and corresponds to exact implementation heads.
• No open blocker is represented as passing through fixture-only or stale evidence.
• The size delta is within the maintainer-accepted budget and the remote/local performance targets are
  met without wrong-tree, stale-tree, lease, or interaction regressions.

Worker stop conditions

• Stop if refactor(ios): converge Appium and Limrun acquisition adapters #2195 or perf(ios): optimize observation lifecycle and prove proxy parity #2198 is incomplete; do not finish their semantics here.
• Stop if deletion changes another platform/provider/physical-device contract.
• Stop if a baseline would need bulk regeneration or a structural allowlist.
• Do not close iOS snapshot backend convergence and fast Simulator observation #2188 until every child issue and exact-head evidence set is verified.