refactor(tp)!: implement retained reactive runtime
Replace the legacy managed layer renderer with one independent retained/reactive text runtime. TP now owns exact dependencies, stable objects, marker-backed mounts, property contribution composition, atomic publication, rollback, and direct text-property facades without ECSS or Ebox dependencies.\n\nBREAKING CHANGE: remove tp-render, tp-stack, scan-driven managed layers, inline runtime metadata, TP-owned CSS cascade APIs, and dollar-variable declarations.\n\nVerified: 290/290 ERT, shuffled 290/290 (seed 20260806), 8/8 doctests, WERROR compile-all, checkdoc, package-lint, diff-check, and isolated TP-only load.
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