feat(decentralize): interactive TUI + deploy-flow integration

.changeset/decentralize-interactive.md

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+---
+"playground-cli": minor
+---
+
+`dot decentralize` is now interactive when invoked with no `--site` flag.
+Running `dot decentralize` on its own opens a TUI that walks through a
+short flow — a yellow "about this command" callout explaining that the
+command mirrors a live static site (https URL) and republishes it as a
+.dot site, then prompts for the site URL, a signer (dev / your phone),
+and a `.dot` name. Domain availability is checked inline against the
+chain (same path as `dot deploy`); leaving the name blank auto-generates
+a free hostname-derived label as before. The pipeline then runs the same
+mirror + Bulletin upload + DotNS register the headless path uses, and
+prints a final summary card with the live URL, IPFS CID, and gateway.
+
+`dot decentralize --site=…` (with or without `--dot` / `--suri`) keeps
+the existing headless contract — the demo service that passes
+`--suri=//Bob` is unchanged.