Adopt Kotlin collection literals across src and test

[pambrose]

Summary

Enables the experimental Kotlin collection-literals feature (via the -Xcollection-literals compiler flag) and converts eligible call sites to [...] literal syntax across src and test:

• emptyList() → []
• listOf(...) → [...]
• mutableListOf(...) → [...], adding an explicit MutableList<T> type on the declaration so mutability is never inferred away

191 conversions across 61 Kotlin files.

Notes & judgment calls

• Content DSL is unaffected. The flag applies to project sources only, not the JSR-223 script engine that evaluates content at runtime — DSL content files keep listOf()/mutableListOf(). (Content.kt had zero call sites anyway.)
• EmptyListDefaultTest left as-is. It exists to verify emptyList()'s own semantics (singleton identity, default-parameter behavior); rewriting its body to [] would leave test names asserting things about emptyList() while no longer calling it.
• TestSupport.formData() gains an explicit MutableList return type. It had an inferred return type and callers mutate the result (data += ...), so converting the body alone would have silently degraded MutableList → List.
• Ineligible sites skipped. Positions where the element type can't be inferred (e.g. Kotest's Any?-typed shouldBe) are correctly left untouched — the compiler is the authority.

Scope note

This branch also carries the pre-existing, already-uncommitted toolchain bumps that were in the working tree (Kotlin 2.4.10, kotlinter 5.6.0, utils 3.2.0, and the root Dokka config refactor). The -Xcollection-literals flag lives alongside the Dokka refactor in build.gradle.kts and can't be cleanly split at the file level, and the green build was verified against this exact combination.

Verification

• compileKotlin / compileTestKotlin (forced --rerun-tasks): clean
• lintKotlinMain / lintKotlinTest + detekt: clean (both parse the new syntax)
• ./gradlew check: 364 tests, 0 failures
• A custom Kotlin lexer audited every changed file: the set of string literals and comments is byte-identical to the base — no [...] inside a string or comment was ever altered.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 52.17391% with 33 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...e/src/main/kotlin/com/readingbat/common/Metrics.kt	0.00%	20 Missing ⚠️
...ain/kotlin/com/readingbat/server/ConfigureOAuth.kt	0.00%	2 Missing ⚠️
...lin/com/readingbat/server/routes/SysAdminRoutes.kt	0.00%	2 Missing ⚠️
...src/main/kotlin/com/readingbat/utils/ScriptTest.kt	0.00%	2 Missing ⚠️
.../src/main/kotlin/com/readingbat/common/Property.kt	50.00%	1 Missing ⚠️
...n/kotlin/com/readingbat/pages/LanguageGroupPage.kt	0.00%	0 Missing and 1 partial ⚠️
...c/main/kotlin/com/readingbat/pages/SessionsPage.kt	0.00%	1 Missing ⚠️
...in/com/readingbat/pages/SystemConfigurationPage.kt	0.00%	1 Missing ⚠️
...otlin/com/readingbat/server/ws/ChallengeGroupWs.kt	0.00%	1 Missing ⚠️
.../kotlin/com/readingbat/server/ws/ClassSummaryWs.kt	0.00%	1 Missing ⚠️
... and 1 more

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