refactor(server): colocate Docker driver config construction with Podman/K8s

[r3v5]

Summary

• Move Docker config construction from cli.rs into lib.rs to match the pattern used by Podman and Kubernetes drivers
• Docker config is now built inside build_compute_runtime() via docker_config_from_file() and apply_docker_local_tls_defaults(), eliminating the docker_config parameter from run_server() and build_compute_runtime()
• Colocate docker_config_reads_bind_mount_opt_in_from_driver_table test next to its constructor in lib.rs

Related Issue

Closes #1853

Changes

crates/openshell-server/src/lib.rs

• Add docker_config_from_file() — mirrors podman_config_from_file() / kubernetes_config_from_file()
• Add apply_docker_local_tls_defaults() — mirrors apply_podman_local_tls_defaults()
• Wire Docker branch in build_compute_runtime() to build config inline (matches Podman branch)
• Remove docker_config parameter from run_server() and build_compute_runtime()
• Move Docker config test from cli.rs to lib.rs

crates/openshell-server/src/cli.rs

• Remove build_docker_config() function
• Remove DockerComputeConfig import
• Remove Docker config test (moved to lib.rs)
• Remove docker_config from run_from_args() call site

crates/openshell-server/src/compute/mod.rs

• Fix pre-existing type mismatch in driver_sandbox_spec_from_public test (separate commit)

Testing

• cargo test -p openshell-server — 892 passed
• mise run ci — full green
• cargo clippy — clean
• cargo fmt — clean
• No behavioral change — Docker driver config still inherits from gateway section, merges driver-specific overrides, and applies TLS defaults

Checklist

• Conventional Commits format
• Signed-off-by (DCO)
• No secrets or credentials
• Scoped to issue at hand

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[r3v5]

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[r3v5]

recheck

[elezar]

There is some overlap between this and #1974 (although I think some of the general cleanup is still applicable).