Generate opencode's config from a tracked template, with matching commands, agents and pwswitch

tests/quickshell/declared-dependencies-contract

@@ -59,7 +59,10 @@ SELF_INSTALLED='^(bun|claude|codex|node|npm|pnpm)$'
 # fresh machine to keep five aliases company. Where docker is absent the
 # aliases fail by naming the missing command, which is the honest outcome.
 # Anything added here needs that same property: absence must be loud.
-OPTIONAL='^(docker)$'
+# opencode is the other kind of optional: link-mcp probes for it with
+# `command -v` and writes its config only where someone installed it with
+# opencode's own installer, the same way it treats claude.
+OPTIONAL='^(docker|opencode)$'
 
 # Provided by a package swap rather than a list entry. ffmpeg cannot be a list
 # entry: RPM Fusion's ffmpeg CONFLICTS with the ffmpeg-free that Fedora ships