Baseline: Ludic compiler + toolchain, Phase 1 syntax fixes complete

Self-hosted compiler (selfhost/*.ludic), runtime, examples, editor tooling,
and docs. Phase 1 of the syntax-redesign cohesion pass has landed:
edge-system fix, signature-query, when-alias, and the documentation truth-pass.
Suite green (14/14), C-free bootstrap fixpoint holds.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tools/editors/jetbrains/README.md

@@ -0,0 +1,58 @@
+# Ludic for JetBrains IDEs
+
+Works in IntelliJ IDEA (Community and Ultimate), CLion, GoLand, PyCharm, Rider,
+WebStorm — anything on the IntelliJ Platform 2023.2 through 2026.2
+(`since-build` 232, `until-build` 262.*).
+
+`until-build` 262 is deliberately ahead of the newest released platform — 2025.3
+is build **253**, and no 262 IDE exists yet. That headroom is the point: an
+`until-build` pinned to today's IDE gets the plugin auto-disabled the moment a
+user upgrades.
+
+Two things are machine-checked rather than assumed, because a plugin that
+packages cleanly can still fail to load:
+
+- `./gradlew verifyPlugin` runs JetBrains' own Plugin Verifier over the built
+  artifact against 2025.3 and reports **Compatible**, with no deprecated or
+  scheduled-for-removal API usages.
+- `./gradlew runIde` boots a real IDEA 2025.3 with the plugin installed. The
+  sandbox log line to look for is
+  `Loaded custom plugins: LSP4IJ (0.20.1), Ludic (1.0.0)` in
+  `.intellijPlatform/sandbox/Ludic/IC-2025.3/log/idea.log`.
+
+**If the plugin does not appear in Settings -> Plugins after installing**, the
+cause is almost always that the IDE's build number is outside
+`since-build`..`until-build`. IntelliJ installs the declared dependency (LSP4IJ)
+from Marketplace first and only then rejects the incompatible plugin, so the
+symptom is "LSP4IJ got installed, mine did not". Check **Help -> About** for the
+build number and widen `pluginUntilBuild` in `gradle.properties` to match.
+
+## Building
+
+Gradle must run on **JDK 17–21**. A newer JDK fails with a bare version number
+as the error message, which is not obvious the first time you see it:
+
+```bash
+export JAVA_HOME=$(/usr/libexec/java_home -v 21)     # macOS
+cd tools/editors/jetbrains
+./gradlew buildPlugin        # -> build/distributions/Ludic-1.0.0.zip
+./gradlew runIde             # try it in a sandbox IDE
+```
+
+The first build downloads an IntelliJ IDEA Community distribution (over 1 GB),
+so expect it to take a while; later builds take seconds. Once the cache is warm,
+
+```bash
+LUDIC_TEST_JETBRAINS=1 ./tools/test-tools.sh
+```
+
+includes the plugin build in the toolchain's own test run.
+
+Install the zip with **Settings -> Plugins -> ⚙ -> Install Plugin from Disk**.
+LSP4IJ is a required dependency; the IDE offers to install it for you.
+
+## Settings
+
+**Settings -> Languages & Frameworks -> Ludic** — the path to `ludic-lsp` and to
+`ludicc`. Both default to `build/` under the project root, which is where
+`tools/build-tools.sh` puts them.