fix(client): PR #135 review — T1/T3/H4-H7 blocking + nits

Code changes addressing PR #135 review (Tyre + Hoshe):

- **T3 (blocking):** test_merge_path_flows_sprint37.gd `_load_main_menu`
  and `_load_char_create` now assert the scene loaded instead of silently
  returning. Missing .tscn → red test, not falsely green.
- **T1:** sim_bridge.gd signal `handshake_complete(protocol_version: int)`
  was D-192 residue with no listeners. Drop the int parameter entirely
  and the literal-0 emit.
- **H4:** test_new_game_catalog_snapshot_resolves_loading_state now
  asserts SimBridge.state == CONNECTED terminus, not just the loading
  flag — guarantees full flow completion, not merely flag-clear.
- **H5:** test_protocol_bridge.gd file-level comment refreshed; drops
  reference to removed protocol-version check tests.
- **H6:** test_p0_regressions.gd `_make_snapshot_bytes` comment refreshed
  and version field removed from fixture dict (D-192: not required).
- **H7:** test_merge_path_flows_sprint37.gd `_make_catalog_snapshot`
  drops version field from fixture dict (D-192).

Follow-up tickets filed for reviewer suggestions:
- **T2:** #889 — revive EntityRenderer sprite constants coverage
  (D-044 ENTITY_WIDTH/HEIGHT, asserted by deleted test_sprite_integration).
- **T4:** #890 — UI timeout fallback for bookmark catalog wait in
  main_menu (systemic 'catalog never arrives' class beyond #872's
  TCP-batch race).
- **T5/T6:** #891 — scene-flow test tier docs + test-only reset
  helpers (SimBridge.reset_for_test, MetaStack.reset_for_test) +
  minimal public API on scenes so UI refactors don't break all four
  flow tests simultaneously.

Verification:
- `make lint-client` — no script errors
- `gdlint client/scripts/ client/ui/` — no problems
- `make test-client` — 2428/2488 passing. 60 remaining failures are
  pre-existing, unrelated to sprint 37 (test_dialogue_sprint20 #558
  signals, test_input_roundtrip integration-sans-server, etc.).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

client/tests/test_protocol_bridge.gd

@@ -1,8 +1,8 @@
 ## D-030 Layer 1: Protocol bridge tests for ObserverSnapshot features.
 ## Validates player_stance (D-053) and player_inventory (D-065) decode,
 ## GameState storage, SimBridge test mode, input encoding for stance toggles,
-## protocol version checks, and fixture round-trips.
-## Spec refs: D-053, D-065, D-020, #449
+## and fixture round-trips. Protocol version checks removed per D-192.
+## Spec refs: D-053, D-065, D-020, #449, D-192
 class_name TestProtocolBridge
 extends GdUnitTestSuite