Platform updates prepare all content types in one linked build

When the platform updates itself, it rebuilds every dynamic content type against the new version before taking traffic. That preparation used to drive each rebuild through the type's own live machinery — waking it up, asking it to rebuild itself, and waiting for it to report back. Measurements showed the actual rebuild work summed to well under a minute, while the wake-up round-trips accounted for almost all of the wait — and when another server was unhealthy, a single round-trip could stall for minutes, stretching preparation to hours.

Preparation now works like one linked build: the update gathers every type's source files in a single pass, rebuilds each type directly in the right order, and records the results — the same per-type outputs as before, without any of the round-trips. An update's preparation time now tracks the compile work itself, and an unhealthy neighbouring server can no longer slow it down. Day-to-day editing and compiling of individual types is unchanged, and operators can switch back to the previous behaviour with a configuration setting.