feat(client): protocol v23 — bookmark_catalog decode + bookmark actions (Workstream 3)

Adds client-side wire support for the bookmark catalog (#614) and the
two associated player actions. PROTOCOL_VERSION bumps from 21 to 23:
- v22 (server): RequestBookmarkCatalog + ConfirmBookmark player actions
- v23 (server): bookmark_catalog field on ObserverSnapshot

Decode:
- protocol.gd decode_snapshot extracts optional bookmark_catalog.
  Defensive parse of BookmarkWire fields (id, title, subtitle, flavor,
  default_location, allowed_locations, allowed_locations_cultures,
  career, starting_capital_tractus). Missing or malformed → null.
- snapshot_handler.gd caches the catalog into GameState.bookmark_catalog
  on each snapshot (server pushes on tick 0; re-fetchable via
  RequestBookmarkCatalog).
- GameState gains bookmark_catalog: Array = [] (untyped per autoload
  parse-order discipline; default empty so callers can iterate without
  null checks).

Encode:
- encode_request_bookmark_catalog() — unit variant, sent to trigger a
  re-push if the cached catalog is missing.
- encode_confirm_bookmark(bookmark_id, starting_location_id) — struct
  variant matching server rmp_serde shape. Called from character
  creation on Start (lands in Workstream 6).

Tests:
- 5 new cases in test_protocol.gd: hand-built bookmark_catalog decode
  (all 9 fields asserted), fixture-based decode round-trip, missing-
  field null behavior, RequestBookmarkCatalog encode roundtrip,
  ConfirmBookmark encode roundtrip.
- All 12 existing snapshot fixtures regenerated from server via
  `cargo test --test gen_fixtures -- --ignored`. The new
  snapshot_with_bookmark_catalog.msgpack fixture was generated by the
  same pass.

Verification:
- gdlint clean
- godot --headless --path client --quit — no SCRIPT ERROR
- test_protocol 62/62, test_client_p3 24/24, test_implant_nav_stack
  52/52, test_implant_registry 42/42, test_implant_app_lifecycle 36/36

Workstream 4 (Option A sequencing via loading_screen + SimBridge
connect) lands next.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/tests/test_protocol.gd

@@ -383,3 +383,109 @@ func test_decode_diagonal_fixtures() -> void:
 		assert_that(input.tick).is_equal(100)
 		assert_that(input.action.variant).is_equal(pair[1])
 		assert_that(input.action.data).is_null()
+
+
+# -- v23: BookmarkCatalog decode -----------------------------------------------
+
+func test_decode_snapshot_with_bookmark_catalog() -> void:
+	# Hand-built dict — fixture generation requires server work, skip round-trip (#614).
+	var raw := {
+		"tick": 1,
+		"version": Protocol.PROTOCOL_VERSION,
+		"entities": [],
+		"bookmark_catalog": {
+			"bookmarks": [
+				{
+					"id": "bm_tycoon_arion",
+					"title": "The Arion Run",
+					"subtitle": "Mid-range freight corridor",
+					"flavor": "You have contacts. Use them.",
+					"default_location": "loc_arion_prime",
+					"allowed_locations": ["loc_arion_prime", "loc_vethis_station"],
+					"allowed_locations_cultures": ["arion", "vethis"],
+					"career": "tycoon",
+					"starting_capital_tractus": 50000,
+				},
+			],
+		},
+	}
+	var encoded: Variant = Messagepack.encode(raw)
+	assert_that(encoded.status).is_null()
+
+	var snapshot: Variant = Protocol.decode_snapshot(encoded.value)
+	assert_that(snapshot).is_not_null()
+	assert_that(snapshot.bookmark_catalog).is_not_null()
+
+	var bmc: Dictionary = snapshot.bookmark_catalog
+	assert_that(bmc.has("bookmarks")).is_true()
+	assert_that(bmc["bookmarks"].size()).is_equal(1)
+
+	var bm: Dictionary = bmc["bookmarks"][0]
+	assert_that(bm["id"]).is_equal("bm_tycoon_arion")
+	assert_that(bm["title"]).is_equal("The Arion Run")
+	assert_that(bm["default_location"]).is_equal("loc_arion_prime")
+	assert_that(bm["allowed_locations"].size()).is_equal(2)
+	assert_that(bm["allowed_locations"][0]).is_equal("loc_arion_prime")
+	assert_that(bm["allowed_locations_cultures"][1]).is_equal("vethis")
+	assert_that(bm["career"]).is_equal("tycoon")
+	assert_that(bm["starting_capital_tractus"]).is_equal(50000)
+
+
+func test_decode_snapshot_bookmark_catalog_fixture() -> void:
+	# Cross-language round-trip: Rust-generated fixture (#614).
+	var bytes = _load_fixture("snapshot_with_bookmark_catalog")
+	var snapshot: Variant = Protocol.decode_snapshot(bytes)
+
+	assert_that(snapshot).is_not_null()
+	assert_that(snapshot.bookmark_catalog).is_not_null()
+	var bmc: Dictionary = snapshot.bookmark_catalog
+	assert_that(bmc["bookmarks"].size()).is_greater(0)
+	var bm: Dictionary = bmc["bookmarks"][0]
+	assert_that(bm.has("id")).is_true()
+	assert_that(bm.has("title")).is_true()
+	assert_that(bm.has("allowed_locations")).is_true()
+	assert_that(bm["career"]).is_equal("tycoon")
+
+
+func test_decode_snapshot_no_bookmark_catalog_is_null() -> void:
+	# Snapshot without bookmark_catalog key → field should be null.
+	var raw := {
+		"tick": 2,
+		"version": Protocol.PROTOCOL_VERSION,
+		"entities": [],
+	}
+	var encoded: Variant = Messagepack.encode(raw)
+	var snapshot: Variant = Protocol.decode_snapshot(encoded.value)
+	assert_that(snapshot).is_not_null()
+	assert_that(snapshot.bookmark_catalog).is_null()
+
+
+# -- v23: RequestBookmarkCatalog + ConfirmBookmark encoding --------------------
+
+func test_encode_request_bookmark_catalog_roundtrip() -> void:
+	var bytes := Protocol.encode_request_bookmark_catalog()
+	assert_that(bytes.size()).is_greater(0)
+
+	var raw: Variant = Messagepack.decode(bytes)
+	assert_that(raw.status).is_null()
+	assert_that(raw.value is Array).is_true()
+	assert_that(raw.value.size()).is_equal(1)
+
+	var entry: Dictionary = raw.value[0]
+	assert_that(entry["action_name"]).is_equal("RequestBookmarkCatalog")
+	assert_that(entry.get("action_data")).is_null()
+
+
+func test_encode_confirm_bookmark_roundtrip() -> void:
+	var bytes := Protocol.encode_confirm_bookmark("bm_tycoon_arion", "loc_arion_prime")
+	assert_that(bytes.size()).is_greater(0)
+
+	var raw: Variant = Messagepack.decode(bytes)
+	assert_that(raw.status).is_null()
+	assert_that(raw.value is Array).is_true()
+
+	var entry: Dictionary = raw.value[0]
+	assert_that(entry["action_name"]).is_equal("ConfirmBookmark")
+	var data: Dictionary = entry["action_data"]
+	assert_that(data["bookmark_id"]).is_equal("bm_tycoon_arion")
+	assert_that(data["starting_location_id"]).is_equal("loc_arion_prime")