Fix Update Packages workflow failures; add Gradle and Mix ecosystem support - #65

What's broken today

The daily "Update Packages" workflow is failing across most of the org. Diagnosed each failure individually across ~10 affected repos; three root causes are fixable here in the shared workflow:

1. Yarn immutable installs (Chronicle.TypeScript): GitHub Actions sets CI=true, which makes Yarn Berry default to immutable installs. The yarn install meant to write the lockfile after npm-check-updates bumps package.json refuses ("lockfile would have been modified... explicitly forbidden").
2. typescript 6→7 vs. Yarn's compat patch (Fundamentals, Components, Workshops): npm-check-updates -u jumps typescript across its 6→7 rewrite (new internal package layout). Yarn Berry's builtin compat/typescript patch hasn't caught up and crashes on install.
3. dotnet package update hard-aborts on per-TFM version divergence (Arc): exits non-zero with zero changes applied whenever a package has different centrally-managed versions per target framework — which is exactly what Arc's conditional Directory.Packages.NET8-9.props setup does deliberately (documented workaround for a Chronicle bug). The command can't reconcile that, so it's failed the same way every day with nothing anyone can do about it via NuGet alone.

(Other failures — ProtocolGeneration, VerticalSlices, cli — were genuine breaking major-version bumps in application code, not workflow bugs; fixed directly in those repos: Cratis/ProtocolGeneration#8, Cratis/VerticalSlices#13, Cratis/cli#71.)

Fixes

• YARN_ENABLE_IMMUTABLE_INSTALLS: false on the post-ncu yarn install step.
• Exclude typescript from the automatic bump (-x typescript) until Yarn ships a compat-patch update for the new TS7 layout.
• Treat dotnet package update's "is not supported by this command" (per-TFM divergence) as a soft skip instead of a hard failure.

New: Gradle (Kotlin/JVM) and Mix (Elixir) support

Adds two new detected ecosystems alongside the existing NuGet/NPM:

• Gradle: detected via a root gradlew + settings.gradle(.kts)/build.gradle(.kts). Runs ./gradlew useLatestVersions (via gradle-versions-plugin + gradle-use-latest-versions-plugin, which the target repo declares itself — companion PR: Enable automated dependency updates via gradle-versions-plugin Chronicle.Kotlin#47) then ./gradlew build to verify.
• Mix: detected via a mix.exs up to 3 directories deep (Elixir repos here nest the package, e.g. Source/chronicle/mix.exs, rather than rooting it), ignoring deps//_build/. Runs mix deps.update --all (respects the ~> constraints already declared in mix.exs) then mix compile to verify.

Both follow the existing NuGet/NPM pattern: only commit and push if the post-update build actually succeeds.

To take effect, Chronicle.Kotlin needs Cratis/Chronicle.Kotlin#47 merged first (declares the two Gradle plugins this relies on). Chronicle.Elixir needs no repo-side changes — mix.exs constraints there are already loose enough for mix deps.update --all to work as-is (verified locally). Chronicle itself is NuGet-only and already works; no changes needed there.

Test plan

• YAML validated (python3 -c "import yaml; yaml.safe_load(open(...))")
• Reproduced the Arc dotnet package update per-TFM abort locally against a real clone and confirmed the new soft-skip branch matches the actual error text
• Reproduced the Gradle useLatestVersions + build cycle locally against a real Chronicle.Kotlin clone (including the stable-only filter correctly skipping a real prerelease build)
• Reproduced the Mix deps.update --all + compile cycle locally against a real Chronicle.Elixir clone
• First live scheduled run against each affected repo (will need to monitor after merge)