scheme: add --json flag to list-presets, --accent flag, drop :accent from preset spec

- list-presets --json outputs structured JSON with variants,
  modes, accents, and default_accent for accent-aware schemes
- --accent flag replaces :accent shorthand in preset string
- Validate --accent against variant's available accents
- resolve_preset returns tuple[str, str] (scheme + variant only)
- Update tests for new signature

cli/src/zshell/subcommands/scheme.py

@@ -21,8 +21,26 @@ app = typer.Typer()
 
 
 @app.command()
-def list_presets():
+def list_presets(
+    json_format: bool = typer.Option(False, "--json", help="Output in JSON format"),
+):
     schemes = list_schemes()
+    if json_format:
+        out = {}
+        for sid, meta in sorted(schemes.items()):
+            variants = {}
+            for v in meta.variants:
+                entry = {"modes": sorted(v.modes)}
+                if v.accents:
+                    entry["accents"] = sorted(v.accents)
+                    entry["default_accent"] = sorted(v.accents)[0]
+                variants[v.id] = entry
+            out[meta.name] = {
+                "id": sid,
+                "variants": variants,
+            }
+        print(json.dumps({"presets": out}, indent=2))
+    else:
         for sid, meta in sorted(schemes.items()):
             var_list = []
             for v in meta.variants:
@@ -41,10 +59,9 @@ def generate(
     scheme: Optional[str] = typer.Option(
         None, help="Color scheme algorithm to use for image mode. Ignored in preset mode."
     ),
-    preset: Optional[str] = typer.Option(
-        None, help="Name of a premade scheme in this format: <scheme>:<variant>[:<accent>]"
-    ),
+    preset: Optional[str] = typer.Option(None, help="Name of a premade scheme in this format: <scheme>:<variant>"),
     mode: Optional[str] = typer.Option(None, help="Mode of the preset scheme (dark or light)."),
+    accent: Optional[str] = typer.Option(None, help="Accent for schemes that support it (e.g. mauve)."),
 ):
 
     HOME = str(os.getenv("HOME"))
@@ -473,8 +490,17 @@ def generate(
         scheme_class = get_scheme_class(scheme)
 
         if preset:
-            p_scheme, p_variant, p_accent = resolve_preset(preset)
-            palette_obj = get_palette(p_scheme, p_variant, mode or config_mode, accent=p_accent)
+            p_scheme, p_variant = resolve_preset(preset)
+            schemes = list_schemes()
+            if accent and p_scheme in schemes:
+                meta = schemes[p_scheme]
+                var_accents = next((v.accents for v in meta.variants if v.id == p_variant), ())
+                if accent not in var_accents:
+                    available = ", ".join(var_accents) if var_accents else "none"
+                    raise typer.BadParameter(
+                        f"Accent '{accent}' not available for '{p_scheme}:{p_variant}'. Available accents: {available}"
+                    )
+            palette_obj = get_palette(p_scheme, p_variant, mode or config_mode, accent=accent)
             colors = palette_obj.colors
             effective_mode = palette_obj.mode
             name = palette_obj.scheme

cli/src/zshell/utils/schemepalettes.py

@@ -132,12 +132,10 @@ def list_schemes() -> dict[str, SchemeMeta]:
     return dict(SCHEMES)
 
 
-def resolve_preset(spec: str) -> tuple[str, str, str | None]:
+def resolve_preset(spec: str) -> tuple[str, str]:
     parts = spec.split(":")
-    if len(parts) == 3:
-        return parts[0], parts[1], parts[2]
     if len(parts) == 2:
-        return parts[0], parts[1], None
+        return parts[0], parts[1]
     if len(parts) == 1:
-        return parts[0], "default", None
-    raise ValueError(f"Invalid preset spec '{spec}'. Use <scheme>:<variant>[:<accent>]")
+        return parts[0], "default"
+    raise ValueError(f"Invalid preset spec '{spec}'. Use <scheme>:<variant>")

cli/tests/test_schemepalettes.py

@@ -154,13 +154,14 @@ class TestListSchemes:
 
 class TestResolvePreset:
     def test_two_parts(self):
-        assert sp.resolve_preset("gruvbox:medium") == ("gruvbox", "medium", None)
+        assert sp.resolve_preset("gruvbox:medium") == ("gruvbox", "medium")
 
     def test_three_parts(self):
-        assert sp.resolve_preset("catppuccin:mocha:mauve") == ("catppuccin", "mocha", "mauve")
+        with pytest.raises(ValueError, match="Invalid preset spec"):
+            sp.resolve_preset("catppuccin:mocha:mauve")
 
     def test_one_part(self):
-        assert sp.resolve_preset("default") == ("default", "default", None)
+        assert sp.resolve_preset("default") == ("default", "default")
 
     def test_edge_spaces(self):
-        assert sp.resolve_preset(" catppuccin : mocha : mauve ") == (" catppuccin ", " mocha ", " mauve ")
+        assert sp.resolve_preset(" catppuccin : mocha ") == (" catppuccin ", " mocha ")