Capabilities plan review and rewrite

Please carefully check our master planning docs and compare them against the downloaded capabilities plan.

The thesis is strong, but the plan needs to be rewritten against the current `10x-product` monorepo, service names, and runtime-source model.

Please proceed with the rewrite using your best judgment.

Rewrote the plan into the current repo topology and tied the rollout to the existing first serious slice instead of a greenfield restart.

We should also think about how to preserve the full AI conversation and highlighted outputs for future engineering planning work.

Recommended a thread-first model with promoted artifacts and briefs, which became the basis for `plan.10xteam.io`.