Rework the UI on Crusenho's pack; credit it in the game, not just the repo

Crusenho's Complete UI Essential Pack is CC BY 4.0 -- redistributable and
commercial-friendly, confirmed from the License.txt the pack itself ships --
so unlike the two bdragon packs a subset is committed: twelve PNGs, 48 KB,
under assets/sprites/ui/. Only what is used, because each committed PNG costs
a Godot .import sidecar and a directory nothing references is one nobody
prunes.

UiTheme builds a Theme in code from it -- button states, panels, line edits --
and every screen roots itself through UiTheme.themed_root(). The HUD's bars are
the pack's frame with a tinted fill, drawn as three horizontal slices because
Godot's nine-patch lives on nodes and the HUD is drawn rather than built from
controls. Inventory slots use the pack's slot art at exactly twice the source
size; a non-integer scale on a 1px border reads as a wobble along every edge.

The credits screen is the other half of the request and it is a licence
obligation, not a nicety: two packs are now CC BY, which asks for attribution
"in any reasonable manner", and a markdown file in a source repo is not
reasonable for someone who downloaded a build. Settings -> Credits shows every
source with its terms and a link to the licence text. test_credits.gd asserts
CREDITS.md and docs/ASSETS.md name every entry, so the three cannot drift.

Two things found by actually looking at the screen, which is the point:

  - The FIRST version of this styled nothing. A Control inherits its theme from
    Control ANCESTORS only, and the chain breaks at the first plain Node or
    CanvasLayer -- which is every screen here. get_window().theme set the
    property, changed nothing, and read as correct. check.sh, 458 tests and a
    clean smoke run all passed with the entire interface unstyled. The theme
    test now instantiates every screen and asks what its buttons resolve.
  - The settings screen showed Fire bound to the right mouse button, because
    the test suite was writing the player's real user://settings.cfg --
    rebinding calls save() and nothing had redirected the path. Settings.path
    is now redirectable, the fixture points it at a scratch file, and a test
    asserts the default is still the player's own.

tools/screenshot.tscn is what found both. It boots the client windowed and
saves the menus, the HUD, settings and credits. Manual, needs a display, and
the only thing in the project that can tell you the interface rendered.

check.sh clean, 460 tests, SMOKE PASS, all four diagnostics green.

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

docs/ROADMAP.md

@@ -20,13 +20,17 @@ 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` | 439 GUT tests, no SceneTree | ~4s |
+| `tools/test.sh` | 460 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 |
 | `diag_loot.tscn` | drop → snapshot → pick up → persist → use → drop, and both loot visibilities on the wire | ~10s |
 | `diag_upgrades.tscn` | level → banked choice → refused in a dungeon and away from the NPC → taken → new stats → persisted → **survives every zone change** | ~10s |
 
+`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/`.
+
 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,
 nor walk to the quartermaster), and a listen server cannot drift its own clock
@@ -129,8 +133,10 @@ play off server events. Enough to prove the pipeline, not a finished look.
 | Impact/death VFX animation | todo | `Art.IMPACT` is loaded and validated but nothing plays it yet |
 | 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/` |
+| 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** | **todo** | Not cosmetic: the SFX are CC BY 4.0 and attribution is a licence *requirement*. [CREDITS.md](../CREDITS.md) is not reachable by a player. |
+| **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. |
 | Replace the two non-redistributable packs | todo | Bullet and FX art is local-only and non-commercial. CC0 replacements would let them into the repo and unblock a commercial release. See [ASSETS.md](ASSETS.md). |
 
 ## Stage 2 — Characters, persistence, levels · *done*