[iterate-4A] intro-video: re-baseline boot golden 50M -> 200M after clock fix

The clock fix (INSTRUCTIONS_PER_MS 10_000 -> 1_000_000, commit 645feb8) moves
the worker-hub +66 ms render gate from ~660k to ~66M instructions, so the old
-n 50M anchor is now pre-render (swaps=0) and no longer guards boot rendering.

Re-anchor sylpheed_n50m -> sylpheed_n200m: at -n 200M the fixed build renders
steadily (draws=3165, swaps=895) and the stable digest is deterministic across
repeated inline lockstep runs. Renames the golden, updates the test's -n and
doc comment, and refreshes tests/golden/README.md. Per the README's re-baseline
policy (intentional digest move -> separate commit).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/xenia-app/tests/golden/sylpheed_n200m.json

@@ -0,0 +1,10 @@
+{
+  "instructions": 200000239,
+  "imports": 575447,
+  "unimpl": 0,
+  "draws": 3165,
+  "swaps": 895,
+  "unique_render_targets": 2,
+  "shader_blobs_live": 6,
+  "texture_cache_entries": 1
+}