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/ASSETS.md

@@ -12,22 +12,24 @@ can be referenced from a scene or script. Files are copied into `res://assets/`
 in game-ready form, and only then imported. The tree is 3.9 GB and
 `tools/check.sh` runs `--import`, which would otherwise walk all of it every run.
 
-What is in the game today totals **548 KB** across seven files: three sprite
-sheets and four sounds. Sprite rects and sound paths are all declared in one
+What is in the game today is three sprite sheets, four sounds and twelve small
+UI sprites. Sprite rects and sound paths are all declared in one
 place, [src/view/art.gd](../src/view/art.gd), and
 `tests/unit/test_art.gd` asserts every rect lands inside its texture — a wrong
 atlas coordinate does not error, it silently draws the wrong pixels.
 
 ## Licence findings
 
-Checked against each pack's itch.io page. **Two of the four forbid
-redistribution**, which is what publishing a repository containing them would
-be — so they are not in the repository.
+Checked against each pack's itch.io page, and against the licence file the pack
+itself ships where there is one. **Two of the five forbid redistribution**,
+which is what publishing a repository containing them would be — so they are not
+in the repository.
 
 | Pack | Licence | Commercial | Credit | In this repo? |
 | --- | --- | --- | --- | --- |
 | [0x72 DungeonTileset II](https://0x72.itch.io/dungeontileset-ii) | **CC0 1.0** (public domain) | Yes | Not required | **Yes** — `assets/sprites/dungeon_tileset.png` |
 | [Helton Yan Pixel Combat](https://heltonyan.itch.io/pixelcombat) | **CC BY 4.0** | Yes | **Required** | **Yes** — `assets/audio/sfx/` |
+| [Complete UI Essential Pack](https://crusenho.itch.io/complete-ui-essential-pack) | **CC BY 4.0** | Yes | **Required** | **Yes** — `assets/sprites/ui/` |
 | [Fire Pixel Bullet 16x16](https://bdragon1727.itch.io/fire-pixel-bullet-16x16) | Custom | Free tier non-commercial; **paid tier allows commercial** | Encouraged | **No, at any tier** — local only |
 | [750+ Effect and FX Pixel All](https://bdragon1727.itch.io/750-effect-and-fx-pixel-all) | Custom | Free tier non-commercial; **paid tier allows commercial** | Encouraged | **No, at any tier** — local only |
 
@@ -56,12 +58,30 @@ passes 156/156 and the game runs.
 This is also why nothing there may be `preload()`ed — `preload` resolves at
 compile time and would fail the build on every machine that lacks the files.
 
+### The UI pack is the easy case
+
+Crusenho's *Complete UI Essential Pack* ships its own `License.txt` naming
+CC BY 4.0 outright, with the licensor and store link spelled out. That permits
+redistribution and commercial use, so unlike the bullet and FX packs a subset of
+it is committed — twelve PNGs, 48 KB, under `assets/sprites/ui/`, listed in
+`UiTheme.TEXTURES`.
+
+Only what the game uses was copied rather than all 98 sprites: each committed
+PNG costs a Godot `.import` sidecar, and a directory of files nothing references
+is a directory nobody prunes. The rest stays in the untracked pack.
+
+The obligation it creates is the same one the audio creates — see below.
+
 ### Two obligations this creates
 
-1. **Helton Yan's CC BY 4.0 requires attribution**, and it is not satisfied by
-   a file in the source tree once the game ships. Players need to be able to
-   see it. [CREDITS.md](../CREDITS.md) records it for now; an in-game credits
-   screen is a todo.
+1. **Two packs are CC BY 4.0 and require attribution** — Helton Yan's audio and
+   Crusenho's UI art. A file in the source tree does not satisfy that once the
+   game ships, because a player who downloaded a build never sees it. **Done:**
+   Settings → Credits shows the same list, built from
+   [src/core/credits.gd](../src/core/credits.gd), including a link to the
+   licence text as CC BY asks. `tests/unit/test_credits.gd` asserts every source
+   there also appears in [CREDITS.md](../CREDITS.md) and in this file, so the
+   three cannot drift apart.
 2. **Both bdragon packs are non-commercial in their free tier.** Buying the
    full tier *does* fix that — confirmed verbatim from the FX pack's paid
    licence: "You may use these assets in personal, commercial or