fix(docker): include experiments/ in builder so workspace manifest parses

[WaylandYang]

Summary

The Dockerfile only copied crates ./crates into the builder stage, but the workspace Cargo.toml lists experiments/v0.4-* as members. Cargo refuses to parse the workspace manifest without their per-crate manifests present, so cargo build --release --bin forkd-controller died with No such file or directory on experiments/v0.4-uffd-wp-poc/Cargo.toml.

This broke release.yml's build + push Docker image job from v0.5.0 through v0.5.2 — the tarball, PyPI, and npm publishes all succeeded each release, but the ghcr.io controller image was never pushed.

Fix

Add COPY experiments ./experiments to the builder stage. Experiments aren't selected by --bin forkd-controller so they don't compile; cargo just needs them present to parse the workspace.

Verification (dev box)

$ docker build -t forkd-controller:test .
[builds clean]
$ docker images forkd-controller:test
forkd-controller   test   4b97d5a97b24   152MB
$ docker run --rm --entrypoint /usr/local/bin/forkd-controller forkd-controller:test --version
forkd-controller 0.5.2

Test plan

• CI green
• After merge: next v* tag push will exercise this in release.yml → ghcr.io/deeplethe/forkd-controller:vX.Y.Z gets pushed for the first time since v0.4

🤖 Generated with Claude Code