fix(theme): drift-guard test, interactive stylebox states, ThemeKeys font consts, richer showcase (whole-branch review)

- build_game_theme.gd: extract build_theme() as a static func returning the
  fully-built Theme; _init() is now a thin save+quit wrapper. Enables a test
  to build a fresh Theme in memory without running the SceneTree main loop.
- test_theme_resource.gd: add test_committed_tres_matches_builder() — builds
  a fresh Theme via the preloaded builder and compares bg_color against the
  committed game_theme.tres for PrimaryCTA/normal, ParchmentCard/panel, and
  DarkPanel/panel. Catches "palette/builder changed, .tres not regenerated."
- build_game_theme.gd: give Tab, TabActive, and Chip explicit hover/pressed/
  focus styleboxes (focus is StyleBoxEmpty to suppress the default ring) so
  they no longer fall back to Godot's default gray button on interaction.
  Add a disabled stylebox + font_disabled_color to PrimaryCTA for the
  unaffordable-CTA state the 2a shell will need.
- theme_keys.gd: add HEADING/ACCENT/MONO font-role consts (kept out of ALL,
  which is stylebox-variation-only); build_game_theme.gd and
  theme_showcase.gd now reference them instead of raw StringName literals.
- theme_showcase.gd: add an italic DM-voice RichTextLabel (EB Garamond
  italic face, spec §6) and two semantic-coloured chips (BLOOD for
  aggressive actions, GOLD for pay/faith) alongside the existing neutral
  chip, demonstrating the script-applied colouring from spec §5.3.
- dark_bay.gdshader: comment noting the stripe uses FRAGCOORD (screen-space)
  while the vignette uses UV (node-local) — intended for full-bleed use.
- surfaces/*.gd: ## comments documenting the accepted deviation from spec
  §5.4 (uniforms set at runtime from Palette rather than baked into the
  .tscn) — no behavior change.
- Regenerated game_theme.tres via build_game_theme.gd.

Full suite: 125/125 (was 124, +1 drift-guard test).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GFDm1ku9WDUacK2S78m2be

client/tests/unit/test_fonts.gd.uid

@@ -0,0 +1 @@
+uid://ck81t1k5xlvgu

client/tests/unit/test_palette.gd.uid

@@ -0,0 +1 @@
+uid://w5blbshxn630

client/tests/unit/test_theme_resource.gd

@@ -2,6 +2,7 @@
 extends "res://addons/gut/test.gd"
 
 const ThemeKeys = preload("res://scripts/theme/theme_keys.gd")
+const Builder = preload("res://scripts/theme/build_game_theme.gd")
 const THEME_PATH := "res://assets/theme/game_theme.tres"
 
 
@@ -27,3 +28,24 @@ func test_cta_has_normal_stylebox():
 func test_default_font_is_set():
 	var t: Theme = load(THEME_PATH)
 	assert_true(t.default_font is FontFile)
+
+
+func test_committed_tres_matches_builder():
+	# Catches "palette/builder changed but nobody regenerated game_theme.tres."
+	# Preloading the builder script and calling its static build_theme() does
+	# NOT run _init() (that only fires on .new()), so this is side-effect-free.
+	var fresh: Theme = Builder.build_theme()
+	var committed: Theme = load(THEME_PATH)
+
+	var checks := [
+		[ThemeKeys.PRIMARY_CTA, &"normal"],
+		[ThemeKeys.PARCHMENT_CARD, &"panel"],
+		[ThemeKeys.DARK_PANEL, &"panel"],
+	]
+	for pair in checks:
+		var variation: StringName = pair[0]
+		var state: StringName = pair[1]
+		var fresh_box: StyleBoxFlat = fresh.get_stylebox(state, variation)
+		var committed_box: StyleBoxFlat = committed.get_stylebox(state, variation)
+		assert_eq(fresh_box.bg_color, committed_box.bg_color,
+			"stale game_theme.tres — %s/%s bg_color drifted from the builder; re-run build_game_theme.gd" % [variation, state])