fix(docker): expose process definition build flag

[burhop]

Summary

• expose the existing default-off process-definition frontend flag as a Docker build argument
• preserve the default-off rollback image while allowing the enabled development image to contain the route
• add a focused Docker smoke-contract assertion

Why

PR #117 merged the read-only Process Definition feature, but the production Docker frontend build could not receive VITE_WRIGHT_PROCESS_DEFINITION_VIEW. This bounded correction restores truthful post-merge deployment verification without changing the API, route contract, or default-off behavior.

Validation

• Wright dev push fast gate: passed
• Ruff and format: passed
• MyPy: passed
• Docker MCP bundle tests: 29 passed
• workflow policy tests: 5 passed
• Docker smoke contracts: 14 passed
• prior exact-content enabled and rollback image builds plus browser walkthrough: passed on Windows

Scope

Two files, 9 insertions, 1 deletion. No direct dev push, merge, release, benchmark, or EPP-F02B implementation is included.