feat(template): add ICON_BUILDER constant to TemplateConstants.Fragment (#327)

* feat(template): add ICON_BUILDER constant to TemplateConstants.Fragment

Resolves #258.

Adds `const val ICON_BUILDER = "icon_builder"` to the `Fragment`
object in `TemplateConstants.kt` and updates the two test sites that
were using the hardcoded literal as a fragments-map key to reference
the new constant:

- TemplateEmitterTest.kt (fragments = mapOf(...))
- PlaceholderResolverTest.kt (fragments = mapOf(...))

Docs/TOML occurrences of "icon_builder" are left untouched: those are
user-facing TOML keys or placeholder strings inside templates (e.g.
${template:icon_builder}), not Kotlin fragment-lookup references.

* feat(template): also use Fragment.ICON_BUILDER in TemplateEditorSchema

Per @rafaeltonholo review on #327 - replaces the remaining "icon_builder"
string literals in the website's TemplateEditorSchema.kt with
TemplateConstants.Fragment.ICON_BUILDER, keeping the website in lockstep
with the core Fragment constant rename. Only the two fragment-map usages
were changed; the definitions.imports key stays as a TOML schema string
since it's a user-facing TOML key, not a Fragment reference.

Relying on CI for detekt/build verification - local JVM toolchain not
wired up on this machine.

---------

Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>

Author: mvanhorn

svg-to-compose/src/commonMain/kotlin/dev/tonholo/s2c/emitter/template/TemplateConstants.kt

@@ -23,6 +23,7 @@ object TemplateConstants {
     object Fragment {
         const val PATH_BUILDER = "path_builder"
         const val GROUP_BUILDER = "group_builder"
+        const val ICON_BUILDER = "icon_builder"
         const val CHUNK_FUNCTION_NAME = "chunk_function_name"
         const val CHUNK_FUNCTION_DEFINITION = "chunk_function_definition"
     }

svg-to-compose/src/commonTest/kotlin/dev/tonholo/s2c/emitter/template/TemplateEmitterTest.kt

@@ -93,7 +93,7 @@ class TemplateEmitterTest {
                     $$"    ${template:icon_builder} {$\n        ${icon:body}$\n    }$\n}",
             ),
             fragments = mapOf(
-                "icon_builder" to $$"${def:builder}(name = ${icon:name})",
+                TemplateConstants.Fragment.ICON_BUILDER to $$"${def:builder}(name = ${icon:name})",
             ),
         )
         val fallback = ImageVectorEmitter(noOpLogger, formatConfig)

svg-to-compose/src/commonTest/kotlin/dev/tonholo/s2c/emitter/template/resolver/PlaceholderResolverTest.kt

@@ -1,5 +1,6 @@
 package dev.tonholo.s2c.emitter.template.resolver
 
+import dev.tonholo.s2c.emitter.template.TemplateConstants
 import dev.tonholo.s2c.emitter.template.TemplateContext
 import kotlin.test.Test
 import kotlin.test.assertContains
@@ -66,7 +67,7 @@ class PlaceholderResolverTest {
     fun `resolves template namespace with fragment`() {
         val ctx = createContext(
             iconVars = mapOf("name" to "TestIcon"),
-            fragments = mapOf("icon_builder" to $$"Builder(name = ${icon:name})"),
+            fragments = mapOf(TemplateConstants.Fragment.ICON_BUILDER to $$"Builder(name = ${icon:name})"),
         )
         val result = PlaceholderResolver.resolve($$"${template:icon_builder}", ctx)
         assertEquals("Builder(name = TestIcon)", result)

website/site/src/jsMain/kotlin/dev/tonholo/s2c/website/components/organisms/playground/template/TemplateEditorSchema.kt

@@ -206,7 +206,7 @@ private fun buildIconTemplateInsertValue(): String {
     val body = iconPlaceholder(TemplateConstants.IconVar.BODY)
     val builder = placeholder(
         TemplateConstants.Namespace.TEMPLATE,
-        "icon_builder",
+        TemplateConstants.Fragment.ICON_BUILDER,
     )
 
     // language=TOML
@@ -255,9 +255,9 @@ private fun buildFragmentKeys(): List<TomlKeyInfo> {
             insertValue = "${frag.GROUP_BUILDER} = \"group(rotate = $groupRotate)\"",
         ),
         TomlKeyInfo(
-            key = "icon_builder",
+            key = frag.ICON_BUILDER,
             description = $$"Icon builder fragment. Placeholders: ${$${ns.DEFINITIONS}:*}, ${$${ns.ICON}:*}.",
-            insertValue = "icon_builder = \"$defBuilder(name = \\\"$iconName\\\")\"",
+            insertValue = "${frag.ICON_BUILDER} = \"$defBuilder(name = \\\"$iconName\\\")\"",
         ),
         TomlKeyInfo(
             key = frag.CHUNK_FUNCTION_NAME,