[johnnyhuy]

Problem

TechDocs builds fail with spawn mkdocs ENOENT. The generator is configured with techdocs.generator.runIn: 'local', which spawns the mkdocs CLI as a subprocess of the backend, but mkdocs is not installed anywhere:

• the runtime image does not install it, so the deployed container has the same failure
• scripts/install does not set it up for local development either

Fix

• Dockerfile: install mkdocs + mkdocs-techdocs-core (which pins its own dependency stack, including mkdocs-material) in the run stage as a user install into /root/.local/bin, which is already first on PATH. A mkdocs --version sanity check fails the build early if the toolchain breaks.
• scripts/install: for local development, bootstrap mkdocs into ~/.local/share/backstage-techdocs-venv and link it into ~/.local/bin when missing, with a warning if that directory is not on PATH. Skipped in CI.
• docs/development.md: update the TechDocs section (it referenced a non-existent make dev) and document the spawn mkdocs ENOENT failure mode.

Testing

• Ran the scripts/install bootstrap block against a sandboxed $HOME with ~/.local/bin removed from PATH (fresh machine simulation, stock Python 3.9): venv creation, plugin install, and the mkdocs symlink all work.
• bash -n scripts/install passes.
• The Dockerfile change is exercised by mise run build in CI.

Co-authored-by: opencode-agent[bot] <219766164+opencode-agent[bot]@users.noreply.github.com>