feat(ui): the first-person HUD is one thing, in the game's own hand

The reticle was five white ColorRects, pasted byte-identically into three
level runtime scripts. The vitals were two stock ProgressBars with a flat
colour override, inlined 1200 lines into the movement controller. The ammo
count — the number a shooter's player looks at most — was drawn by the LEVEL,
in a black rounded panel that shared nothing with the menus, and it had a
special case in it (`elif active_weapon is DoubleBarrelShotgun`) because that
weapon never declared a name or a capacity.

Everything that describes A PLAYER now belongs to ui/player_hud.gd, and a
level owns the level. The immediate symptom that fixed: the screen had two
ammo panels on it at once, in two different styles, overlapping in the corner.

What each piece now says, rather than merely shows:

  ui/crosshair.gd    one drawn reticle instead of five rectangles, so it can
                     BLOOM — open with speed, airtime and each shot, snap shut
                     on ADS. That is the accuracy readout of the whole game and
                     five ColorRects could not express it. Every stroke is
                     drawn twice, ink underneath, because a 2 px white line
                     disappears over pale concrete exactly when aim matters.
                     The hit confirmation is the same cross at 45 degrees, so
                     it lands where the eye already is.
  ui/vital_bar.gd    segmented, so remaining health can be COUNTED rather than
                     estimated, with a drain ghost that holds the old value for
                     a beat — the gap between fill and ghost is the size of the
                     hit, which a bar that merely gets shorter never tells you.
  ui/ability_chip.gd dash and grapple as a wipe across a chip rather than a
                     tinted JPEG with a 12 px number under it. A shape changing
                     size is readable in peripheral vision; 12 px type is not.
  chain meter        promoted out of the debug panel. Movement is this game's
                     first stated pillar and chaining is its skill expression,
                     so the count is a score, not a diagnostic.

The numerals moved OFF the bars and beside them. Text centred on a two-tone
bar cannot be given a colour that beats both the fill and the trough — that is
the 2.4:1 debug/ui_contrast_check.gd measured on the old HUD — so this fixes it
at the source rather than leaning on an outline to rescue it.

debug/hud_layout_check.gd measures where every element actually lands, which is
how three real bugs were found rather than squinted at: `set_anchors_preset`
moves the anchors and LEAVES THE OFFSETS, so the reticle spanned the viewport
with a size of exactly (0,0) and drew itself in the top-left corner; a
PRESET_CENTER applied after the ring's own `_ready` undid its centring; and a
BOX CONTAINER's own `alignment` is what pushes content to an edge, not a
SHRINK_END flag on the box, whose minimum width depends on children that may be
hidden. The ammo card was hanging off the right edge of the screen because of
the last one.

DoubleBarrelShotgun now declares `weapon_name` and `max_shells` like every
other weapon, and the four inline `2`s are gone.

spawn smoke 0 failures, 11/11 movement tests, contrast 108/108, layout PASS.

Co-Authored-By: Claude Opus 5 <[email protected]>

weapons/double_barrel_shotgun.gd

@@ -3,7 +3,17 @@ class_name DoubleBarrelShotgun
 
 @export var reload_time: float = 1.0
 
-var shells: int = 2
+## The name and the capacity every other weapon in the set declares.
+##
+## This one did not, and it had "2" written inline in four places. The HUD had no
+## way to ask how big a full load was, so the level's ammo panel carried a
+## special case — `elif active_weapon is DoubleBarrelShotgun` — to fill in the
+## name, and the capacity was simply hardcoded there as well. Anything that ever
+## wanted to display this weapon had to know about it specifically.
+@export var weapon_name: String = "Double Barrel"
+@export var max_shells: int = 2
+
+var shells: int = max_shells
 var reloading: bool = false
 var reload_timer: float = 0.0
 var _vm_kick: float = 0.0
@@ -59,7 +69,7 @@ func _process(delta: float) -> void:
 	if reloading:
 		reload_timer -= delta
 		if reload_timer <= 0.0:
-			shells = 2
+			shells = max_shells
 			reloading = false
 
 	# Big single-shot shove that springs back.
@@ -77,7 +87,7 @@ func _input(event: InputEvent) -> void:
 		_try_fire()
 	
 	if event.is_action_pressed("reload"):
-		if shells < 2 and not reloading:
+		if shells < max_shells and not reloading:
 			_start_reload()
 
 func _start_reload() -> void: