Fix bullet/ship desync; rework death, escape, arrival and hub awareness

(1) Bullets appeared to trail the ship. Two independent causes, measured with
the new tools/diag_prediction.gd rather than guessed at:
  - ServerRuntime ticked before ClientRuntime, so input sampled on frame N was
    not consumed until frame N+1, leaving the drawn ship a constant one tick
    (4.00px at 240 u/s) ahead of the authoritative one that bullets spawn from.
    ClientRuntime now sets process_physics_priority = -10. Gap on a listen
    server: 4.00px -> 0.10px mean, 0.30px worst.
  - PLAYER_MUZZLE_OFFSET was PLAYER_RADIUS + 6 = 12px against a 13px drawn
    ship, so bullets were born inside the sprite. Regression from the previous
    commit's hitbox shrink; it now derives from PLAYER_VISUAL_RADIUS.

(2) No more timed respawn. A downed player stays down until they ask for the
hub (E), which is an ordinary input -- the server has no "revive me" message.

(3) Escape channel 3s -> 1s, and damage no longer cancels it. An interruptible
channel makes killing the process strictly better than using the button, so a
dropped connection now runs the same channel: the player stays in the world as
linkdead, still killable, and is only released once it completes. Instances
refuse to close while a linkdead body is resolving, or a solo drop would delete
it on the next tick and hand the exploit straight back.

(4) Escape opens an in-game menu: return to hub (routed through the same held-
escape channel, not a new message), disconnect, quit.

(5) Server pushes a roster so the hub shows who is online and which dungeon
they are in. Entering a dungeon grants 2s arrival protection -- invulnerable
AND weapons-cold, since invulnerability alone would make the spawn a free
firing position -- flagged in the snapshot and drawn on every protected ship.

(6) Cleared dungeons hold the party 30s (was 5s) with a visible countdown.

(7) The hub's grey circle was a 100k-HP target dummy that read as scenery. Now
drawn as a bullseye so its purpose is legible.

Protocol version 1 -> 2. 91 tests (was 78); smoke.sh gains a bot that is
SIGKILLed mid-dungeon to prove the disconnect path end to end. check.sh,
test.sh and smoke.sh all pass.

tests/unit/test_net_codec.gd

@@ -11,7 +11,7 @@ func before_each() -> void:
 	p.pos = Vector2(120.5, -64.25)
 	p.aim = 1.25
 	p.hp = 73
-	p.escape_ticks = 90
+	p.escape_ticks = 30
 	p.last_input_tick = 555
 	world.spawn_enemy(Content.turret(), Vector2(-200.0, 100.0))
 	world.spawn_boss(Content.warden())
@@ -30,7 +30,7 @@ func test_snapshot_round_trips_player_state() -> void:
 	assert_eq(int(rec["last_input_tick"]), 555)
 	assert_true((int(rec["flags"]) & Protocol.F_ALIVE) != 0)
 	assert_true((int(rec["flags"]) & Protocol.F_ESCAPING) != 0)
-	assert_almost_eq(float(rec["escape"]), 90.0 / float(SimConfig.ESCAPE_CHANNEL_TICKS), 0.01)
+	assert_almost_eq(float(rec["escape"]), 30.0 / float(SimConfig.ESCAPE_CHANNEL_TICKS), 0.01)
 
 
 func test_snapshot_carries_enemy_radius_for_late_joiners() -> void:
@@ -105,3 +105,59 @@ func test_truncated_input_packet_is_rejected_not_read_past() -> void:
 
 func test_empty_input_packet_is_safe() -> void:
 	assert_eq(NetCodec.decode_inputs(PackedByteArray()).size(), 0)
+
+
+# --- Roster -----------------------------------------------------------------
+
+func test_roster_round_trips() -> void:
+	var entries: Array[Dictionary] = [
+		{"peer": 7, "name": "ada", "kind": Protocol.InstanceKind.LOBBY,
+			"instance": 1, "alive": true},
+		{"peer": 9, "name": "grace", "kind": Protocol.InstanceKind.DUNGEON,
+			"instance": 4, "alive": false},
+	]
+	var out := NetCodec.decode_roster(NetCodec.encode_roster(entries))
+	assert_eq(out.size(), 2)
+	assert_eq(int(out[0]["peer"]), 7)
+	assert_eq(String(out[0]["name"]), "ada")
+	assert_eq(int(out[0]["kind"]), Protocol.InstanceKind.LOBBY)
+	assert_true(out[0]["alive"])
+	assert_eq(String(out[1]["name"]), "grace")
+	assert_eq(int(out[1]["kind"]), Protocol.InstanceKind.DUNGEON,
+		"the hub needs to know someone is already inside")
+	assert_eq(int(out[1]["instance"]), 4)
+	assert_false(out[1]["alive"])
+
+
+func test_roster_survives_unicode_names() -> void:
+	var entries: Array[Dictionary] = [
+		{"peer": 1, "name": "ゆき", "kind": 0, "instance": 1, "alive": true}]
+	var out := NetCodec.decode_roster(NetCodec.encode_roster(entries))
+	assert_eq(String(out[0]["name"]), "ゆき")
+
+
+func test_empty_roster_is_safe() -> void:
+	assert_eq(NetCodec.decode_roster(PackedByteArray()).size(), 0)
+	assert_eq(NetCodec.decode_roster(NetCodec.encode_roster([] as Array[Dictionary])).size(), 0)
+
+
+# --- Snapshot extras --------------------------------------------------------
+
+func test_snapshot_carries_spawn_grace_and_linkdead_flags() -> void:
+	var p: SimPlayer = world.players[42]
+	p.spawn_grace = 30
+	p.linkdead = true
+	var snap := NetCodec.decode_snapshot(NetCodec.encode_snapshot(world))
+	var flags := int(snap["players"][0]["flags"])
+	assert_true((flags & Protocol.F_SPAWN_GRACE) != 0)
+	assert_true((flags & Protocol.F_LINKDEAD) != 0)
+
+
+func test_cleared_countdown_round_trips() -> void:
+	var snap := NetCodec.decode_snapshot(NetCodec.encode_snapshot(world, 17))
+	assert_eq(int(snap["cleared_countdown"]), 17)
+
+
+func test_countdown_defaults_to_not_applicable() -> void:
+	var snap := NetCodec.decode_snapshot(NetCodec.encode_snapshot(world))
+	assert_eq(int(snap["cleared_countdown"]), Protocol.COUNTDOWN_NONE)