Style the rest of the interface: panels, sliders, scrollbars, cards

Buttons were the easy half. This is everything else.

Dialogs sit on panels now rather than being text over a dimmed world -- the
pause menu, character select, upgrades, settings and credits all root through
UiTheme.dialog_panel(). The panel stylebox is the pack's frame MODULATED DARK.
The set is cream throughout, which is right for buttons and wrong for a dialog
over a dark dungeon; tinting keeps the pixel border and the corner shape and
lets every label the game already draws in light colours stay readable, instead
of recolouring every label in five screens to suit the art.

Sliders and scrollbars are the pack's too, section headings sit on its banner
ribbon, and an upgrade card's rarity is now its frame rather than a word on it
-- three choices are compared at a glance and a colour reads faster than a
label.

Two bugs of the same shape, and neither was findable without looking at the
screen. A Slider and a ScrollBar take their THICKNESS from the stylebox's
minimum size, which for a StyleBoxTexture is its content margins. Mine were
zero, so both resolved the correct stylebox, reported the correct texture, and
drew a groove zero pixels tall. A probe confirmed the theme was resolving
perfectly while the track was invisible. Tests now assert every slider and
scrollbar stylebox has a non-zero minimum, and it is gotcha 7 in CLAUDE.md.

The first attempt at the slider groove also used the pack's HOLLOW bar sprite,
whose middle is transparent -- tinting it dark left an outline and nothing
else. It uses the solid one.

tools/screenshot.tscn gained the upgrade screen, which it has to stage: the
game scene owns that screen's visibility and re-asserts it every frame, so
setting `visible` lasted exactly one frame, and standing the player at the NPC
client-side lasted until reconciliation pulled them back. It now moves the
player on both sides and holds it until the shot. That tool has caught four
bugs the automated gates all passed.

check.sh clean, 468 tests, SMOKE PASS, all four diagnostics green.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/ROADMAP.md

@@ -20,7 +20,7 @@ What "everything passes" currently means. Numbers move; the shape does not.
 | Gate | Covers | Runtime |
 | --- | --- | --- |
 | `tools/check.sh` | every script parses and type-checks | ~5s |
-| `tools/test.sh` | 460 GUT tests, no SceneTree | ~4s |
+| `tools/test.sh` | 468 GUT tests, no SceneTree | ~4s |
 | `tools/smoke.sh` | 23 assertions over a real ENet socket: handshake, auth, character creation and persistence, both dungeon kinds, escape, hard kill, polite disconnect | ~40s |
 | `diag_prediction.tscn` | client-prediction gap, with injected clock drift | ~10s |
 | `diag_progression.tscn` | kill → xp → level → health, death → retire → roster, swap guards | ~10s |
@@ -29,7 +29,14 @@ What "everything passes" currently means. Numbers move; the shape does not.
 
 `tools/screenshot.tscn` is a **manual** check, not a gate: it needs a display,
 and it is the only thing in the project that can tell you the interface
-actually rendered. Run it after touching `src/ui/`.
+actually rendered. Run it after touching `src/ui/`. It captures the main menu,
+the HUD, the pause menu, settings, credits and the upgrade choice — the last of
+those by staging an offer, because earning one would make the shot depend on a
+dungeon run.
+
+It has now caught four bugs that every other gate passed: the theme applying to
+nothing, the test suite rewriting the player's settings, an invisible slider
+track and an invisible scrollbar.
 
 The four diagnostics exist because the smoke test structurally cannot reach
 what they cover: bots are poor shots (so they neither level up, produce drops,
@@ -134,6 +141,8 @@ play off server events. Enough to prove the pipeline, not a finished look.
 | Directional sprites, hit flashes, screen shake | todo | |
 | Rebindable controls | done | [src/ui/settings_screen.gd](../src/ui/settings_screen.gd), [src/core/settings.gd](../src/core/settings.gd) |
 | Themed controls from a UI pack | done | [src/view/ui_theme.gd](../src/view/ui_theme.gd), art in `assets/sprites/ui/` |
+| Dialogs on panels, sliders, scrollbars | done | `UiTheme.dialog_panel`, `HSlider` / `VScrollBar` theme entries |
+| Upgrade cards framed by rarity | done | `UiTheme.card_panel`, `UpgradeScreen._make_card` |
 | Textured HUD bars and inventory slots | done | `HUD._bar`, `HUD._draw_inventory` |
 | Audio buses and a volume setting | done | `Settings`, an SFX bus created at runtime, sliders in the settings screen |
 | **In-game credits screen** | **done** | Settings → Credits, from [src/core/credits.gd](../src/core/credits.gd). Two packs are CC BY 4.0 and attribution is a licence *requirement* — [CREDITS.md](../CREDITS.md) is not reachable by a player. |