ci: run conan recipes / engine build on Linux too

Add an ubuntu-latest leg to both the Build (engine) and Publish Conan
Recipes workflows so Linux is exercised in CI alongside Windows and
macOS, matching the recipes that now declare Linux-x86_64.

The engine's own Linux support is not yet verified, so the Build matrix
sets fail-fast: false to keep the Linux leg from cancelling the Windows
and macOS legs. Publish already had fail-fast: false.

README updated to list Linux among the supported platforms and as a
publish target.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: FlyAndNotDown

.github/workflows/build.yml

@@ -18,8 +18,11 @@ env:
 jobs:
   build:
     strategy:
+      # Linux runs alongside Windows/macOS, but the engine's own Linux support is
+      # not yet verified -- keep a failing Linux leg from cancelling the others.
+      fail-fast: false
       matrix:
-        os: ['windows-2022', 'macOS-latest']
+        os: ['windows-2022', 'macOS-latest', 'ubuntu-latest']
 
     runs-on: ${{ matrix.os }}
 

.github/workflows/publish-conan-recipes.yml

@@ -33,6 +33,8 @@ jobs:
             cppstd: '17'
           - os: macOS-latest
             cppstd: gnu17
+          - os: ubuntu-latest
+            cppstd: gnu17
 
     runs-on: ${{ matrix.os }}
 

ThirdParty/ConanRecipes/README.md

@@ -30,8 +30,8 @@ To build every recipe at once, use the `build_recipes.py` helper. It walks each
 recipe directory, picks the latest version (the top-most entry in
 `conandata.yml`) and builds them one-by-one in dependency order. Each recipe
 lists the platforms it supports under a `platforms` key in its `conandata.yml`
-(currently `Windows-x86_64` and/or `Macos-armv8`); recipes that do not target
-the current host are skipped. If any recipe fails the script stops immediately
+(currently `Windows-x86_64`, `Macos-armv8` and/or `Linux-x86_64`); recipes that
+do not target the current host are skipped. If any recipe fails the script stops immediately
 and prints a summary.
 
 ```shell
@@ -70,8 +70,8 @@ Recipe changes are validated and published automatically:
   the job. A PR can therefore change recipes and engine code together and
   be validated atomically.
 - After a push to `master` that touches `ThirdParty/ConanRecipes`, the
-  `Publish Conan Recipes` workflow builds the changed recipes on Windows
-  and macOS and uploads them to the remote (credentials come from the
+  `Publish Conan Recipes` workflow builds the changed recipes on Windows,
+  macOS and Linux and uploads them to the remote (credentials come from the
   `CONAN_REMOTE_USER` / `CONAN_REMOTE_PASSWORD` repository secrets). It can
   also be re-run manually via `workflow_dispatch` if an upload failed.