ci(internal-workflows): test File Browser sidecar

[homelab-agent-bot]

What

• enable Coder's wildcard application URL in the disposable Compose control plane
• verify the File Browser sidecar agent connects and reports a healthy Coder application
• prove the Coder agent remains PID 1 and owns the File Browser process lifecycle
• prove both containers share the selected home PVC by overwriting a workspace-owned file from the sidecar
• fetch the UI and one generated static asset through Coder's owner-only subdomain proxy

Why

Pod health alone would not prove the feature works through Coder, and creating a new file would not prove File Browser can modify ordinary workspace-owned files. These assertions cross every boundary the feature depends on: agent transport, process ownership, filesystem identity, persistent-volume selection, application health, and browser asset routing.

File Browser uses root-relative assets, so the test control plane needs the same wildcard application mode required by the shipped template.

Dependency

Stacked on PR #928, the File Browser workspace app. Once that PR lands, this PR should be retargeted to main.

Validation

• pre-commit run --all-files
• independent subagent review, with the original permission test strengthened from directory-level creation to same-file overwrite