Fix lobby/HUD UI pinned at (0,0); shrink player hitbox below visual size

The lobby connect menu and three pieces of the HUD (hit-flash overlay, boss
bar centering, death-message centering, hint label) were all silently broken
by the same Godot gotcha: set_anchors_preset(preset) with the default
keep_offsets=false does NOT zero the offsets to the preset's margins -- it
recomputes them to preserve the control's *current* rect, which for a
freshly constructed Control is (0,0). Anchors end up correct; the actual
rect stays pinned to the top-left corner regardless. Fixed by switching to
set_anchors_and_offsets_preset() everywhere a Control is built in code, and
by using offset_left/offset_top (anchor-relative) instead of .position
(absolute) for the HUD hint label. Documented as gotcha #5 in CLAUDE.md.

Also split PLAYER_RADIUS into two constants: PLAYER_RADIUS (6.0, the
authoritative hitbox used by SimWorld) and PLAYER_VISUAL_RADIUS (13.0,
view-only, used by world_view.gd). The client renders every ship a little
late relative to the server -- interpolation delay, reconciliation
smoothing -- so a hitbox that matched the sprite would let bullets connect
against a ship the player watched dodge clear of them. A smaller hitbox
means the occasional bullet visibly clips the sprite without a hit, which
reads as more forgiving of latency than the reverse.

Verified headlessly: a throwaway scene instantiating MainMenu/HUD under a
real 1280x720 viewport, asserting the panel is centered and _canvas.size /
hint position resolve correctly, before and after each fix. check.sh,
test.sh (78/78) and smoke.sh all pass.

src/view/world_view.gd

@@ -103,8 +103,13 @@ func _draw_local_player() -> void:
 		_draw_escape_ring(client.predicted_pos, client.my_escape, COL_LOCAL)
 
 
+## Drawn at PLAYER_VISUAL_RADIUS, larger than the PLAYER_RADIUS hitbox actually
+## used for hits -- see the comment on those constants in sim_config.gd. The
+## mismatch is deliberate, not a placeholder: a bullet can visibly clip the
+## sprite without registering a hit, which reads as more forgiving of latency
+## than the reverse.
 func _draw_ship(pos: Vector2, aim: float, col: Color, alive: bool) -> void:
-	var r := SimConfig.PLAYER_RADIUS
+	var r := SimConfig.PLAYER_VISUAL_RADIUS
 	draw_circle(pos, r, Color(col, 0.4 if alive else 0.2))
 	draw_arc(pos, r, 0.0, TAU, 20, col, 2.0)
 	if alive:
@@ -115,5 +120,5 @@ func _draw_ship(pos: Vector2, aim: float, col: Color, alive: bool) -> void:
 ## The escape channel is drawn on the player, not just in the HUD, so other
 ## players can see someone is about to leave and react.
 func _draw_escape_ring(pos: Vector2, progress: float, col: Color) -> void:
-	draw_arc(pos, SimConfig.PLAYER_RADIUS + 8.0, -PI * 0.5,
+	draw_arc(pos, SimConfig.PLAYER_VISUAL_RADIUS + 8.0, -PI * 0.5,
 		-PI * 0.5 + TAU * progress, 32, Color(col, 0.9), 3.0)