chore(deps): update ubuntu docker tag to v26

.devcontainer/Dockerfile

@@ -3,12 +3,13 @@
 # CLAUDE.md's "Devcontainer" section says what it covers and what still needs
 # the host (the Factorio oracle capture).
 #
-# Plain Ubuntu 24.04 (noble), pinned by digest so every rebuild starts from
-# the same bytes. It was the .NET SDK image until the C# was removed; that
-# image is itself noble, so the apt packages below did not change.
+# Plain Ubuntu 26.04 (resolute), pinned by digest so every rebuild starts from
+# the same bytes. It was the .NET SDK image (itself noble, 24.04) until the C#
+# was removed, then plain 24.04; the apt packages below installed unchanged on
+# both moves.
 # Re-pin with:
-#   docker buildx imagetools inspect ubuntu:24.04
-FROM ubuntu:24.04@sha256:68ee22004a9109b44973313b02ff7b1de250f1de0f5ecb628d73f579aaff33ac
+#   docker buildx imagetools inspect ubuntu:26.04
+FROM ubuntu:26.04@sha256:c098726dd9b9733f3e885f8de0ef375206a311b0a317eadc40d347b1115fb944
 
 # The base image already has a `ubuntu` user at uid 1000, so there is no user
 # to create - only sudo to add, for the postCreate chown of the named volumes.

CLAUDE.md

@@ -56,7 +56,7 @@ CI (`.github/workflows/ci.yml`) runs the five Rust check and build commands abov
 
 ### Devcontainer
 
-`.devcontainer/` builds a Linux container carrying every toolchain this repo needs: **Rust 1.99.1 through rustup (with rustfmt, clippy, rust-src and the wasm32 target), Node 24.21.0, python3, git and gcc** (cargo's linker), on plain `ubuntu:24.04` pinned by digest. Node is pinned exactly and checksummed. The base already has user `ubuntu` at uid 1000, which is the container's `remoteUser`. Before stage 13b the image was built on the .NET SDK and also carried dotnet, PowerShell and Lua 5.2; those are gone with the C#.
+`.devcontainer/` builds a Linux container carrying every toolchain this repo needs: **Rust 1.99.1 through rustup (with rustfmt, clippy, rust-src and the wasm32 target), Node 24.21.0, python3, git and gcc** (cargo's linker), on plain `ubuntu:26.04` pinned by digest. Node is pinned exactly and checksummed. The base already has user `ubuntu` at uid 1000, which is the container's `remoteUser`. Before stage 13b the image was built on the .NET SDK and also carried dotnet, PowerShell and Lua 5.2; those are gone with the C#.
 
 **Rust is pre-installed, and `rust/rust-toolchain.toml` still decides.** The image installs the toolchain named by `RUST_VERSION` in the Dockerfile, so creating the container downloads no compiler. Inside `rust/`, rustup reads the toolchain file as it does anywhere else. A stale `RUST_VERSION` therefore breaks nothing - rustup just installs the new pin on first use (about 10 s, measured) - which is exactly why nobody would notice. So the Devcontainer CI job compares `RUST_VERSION` with the toolchain file, checks that `rustc` and `cargo` in `rust/` report that version, and checks that the wasm32 target is installed. **When `rust/rust-toolchain.toml` moves, move `RUST_VERSION` with it.** The toolchain file is in that job's paths filter for this reason.