feat(multiplayer): Phase 5 task 5.1 - match lifecycle state machine

Adds the §6.1 state machine, its broadcast, and the client side that
follows it. Physics, freezing and input are deliberately NOT gated on
state yet - 5.3 and 5.4 own freeze/unfreeze at kickoff and goal, and
doing it here would change the conditions every Phase 4 prediction gate
was measured under.

scripts/match_state.gd holds the enum and transition table as pure data
with no scene or RPC dependency, so the table is checked exhaustively
rather than by example: every state reachable, every state has an exit,
no self-transitions, abort-to-LOBBY from anywhere per §6.4, illegal
shortcuts rejected, unknown values refused rather than coerced. The enum
values are the wire format - match_state has been a u8 in the snapshot
header since §2.4 - so a test pins them; only append, never renumber.

The server validates every transition and push_errors an illegal one
rather than following it. Clients deliberately do NOT enforce the table:
authoritative state must be accepted, and a late joiner legitimately
jumps straight to PLAYING.

Two channels carry the state. state_change (reliable, channel 0) is
prompt and carries an absolute at_tick, never a duration. The snapshot's
match_state byte is the catch-up path for a client not yet sent a
transition - a late joiner, or the window between scene load and the
first RPC.

The byte needs a tick guard, and this was found the hard way. Snapshots
are unreliable_ordered on channel 2 and ordering holds only within a
channel, so a state_change for tick N routinely arrives before an
in-flight snapshot from tick N-2. Without the guard the client applies
the new state then gets dragged back by the older byte, oscillating on
every transition - observed directly as LOADING -> WARMUP -> LOBBY ->
PLAYING -> LOBBY while running a deliberately-broken-byte control. Only
a byte at least as new as match_state_since_tick is accepted.

WARMUP_TICKS/GOAL_PAUSE_TICKS are honest placeholders so 5.1 drives real
transitions to verify against; 5.3 and 5.4 replace them. The server also
leaves LOADING immediately rather than waiting for scene_ready, which
does not exist yet.

New smoke flag --exercise-match-state, passed to both roles: the host
forces a goal to drive a GOAL_PAUSE cycle, the client records the
sequence and asserts every consecutive pair is legal, that ticks are
monotonic, and that the wire byte agrees with its own state. Observed
LOADING -> WARMUP -> PLAYING -> GOAL_PAUSE -> WARMUP with tick deltas
matching the configured durations exactly.

Verified against a control: hardcoding the snapshot byte back to 0 fails
both the byte assertion and the transition-legality assertion. The byte
is asserted separately from the RPC precisely because everything else in
the check is RPC-driven and would pass with a dead byte - the same gap
that hid the Phase 4 label bug (gotcha 47).

Regression: 81 unit tests; 60s free-flight LAN (p99 0.148m, 0 hard
snaps, marker 0/3364); transition gate 0.00%; ball contact; two-bot CI.

Game/tests/networked_match_smoke.gd

@@ -18,6 +18,7 @@ var _drive_seconds := DEFAULT_DRIVE_SECONDS
 var _exercise_ball_contact := false
 var _exercise_free_flight := false
 var _exercise_input_transitions := false
+var _exercise_match_state := false
 var _warmup_seconds := 0.0
 
 
@@ -35,6 +36,8 @@ func _ready() -> void:
 			_exercise_free_flight = true
 		elif arg == "--exercise-input-transitions":
 			_exercise_input_transitions = true
+		elif arg == "--exercise-match-state":
+			_exercise_match_state = true
 		elif arg.begins_with("--warmup-seconds="):
 			_warmup_seconds = maxf(0.0, arg.get_slice("=", 1).to_float())
 
@@ -94,7 +97,7 @@ func _on_host_player_joined(_peer_id: int, _name: String) -> void:
 	get_tree().root.add_child.call_deferred(hooks)
 	# The host must outlive client settle + drive, plus connection/shutdown
 	# slack. This keeps --drive-seconds useful for sustained prediction QA.
-	hooks.run_host_check.call_deferred(_settle_seconds + _warmup_seconds + _drive_seconds + 4.0)
+	hooks.run_host_check.call_deferred(_settle_seconds + _warmup_seconds + _drive_seconds + 4.0, _exercise_match_state)
 
 
 func _on_client_welcomed() -> void:
@@ -103,7 +106,7 @@ func _on_client_welcomed() -> void:
 	get_tree().change_scene_to_file.call_deferred("res://scenes/networked_match.tscn")
 	var hooks := preload("res://tests/networked_match_test_hooks.gd").new()
 	get_tree().root.add_child.call_deferred(hooks)
-	hooks.run_client_check.call_deferred(_settle_seconds, _drive_seconds, _exercise_ball_contact, _exercise_free_flight, _warmup_seconds, _exercise_input_transitions)
+	hooks.run_client_check.call_deferred(_settle_seconds, _drive_seconds, _exercise_ball_contact, _exercise_free_flight, _warmup_seconds, _exercise_input_transitions, _exercise_match_state)
 
 
 func _on_abuser_welcomed() -> void: