docs: refresh root README around the three Stack pillars

.changeset/adapter-readmes-refresh.md

@@ -0,0 +1,22 @@
+---
+'@cipherstash/stack-supabase': patch
+'@cipherstash/stack-drizzle': patch
+'@cipherstash/stack-prisma': patch
+---
+
+Refresh the adapter READMEs (they ship on each package's npm page):
+
+- **stack-supabase**: full rewrite — the old README was a stub. Now covers the
+  introspecting `encryptedSupabase(url, key)` factory, the encrypted filter
+  surface (`eq`/`neq`/`in`/`match`, range, `order()` on OPE-backed columns),
+  the EQL 3.0.2 PostgREST limitations, and the quick start.
+- **stack-drizzle**: fix the hero example — `ops.contains` is encrypted-JSONB
+  containment (a `types.Json` column) and would throw on a text column; the
+  free-text operator is `ops.matches`. The operator table no longer lists
+  `contains` under free-text match.
+- **stack-prisma**: correct the encrypted-column-type catalog (domain-named
+  factories across text/integer/float/numeric/date/timestamp/boolean/JSON, not
+  "six types"), fix the authentication docs URL, and replace relative links
+  (which 404 on npm) with absolute ones.
+- All three: add the badge header and the architecture diagram from the root
+  README.

.changeset/stack-readme-single-source.md

@@ -0,0 +1,9 @@
+---
+'@cipherstash/stack': patch
+---
+
+The npm README for `@cipherstash/stack` is now the root Stack README — the
+package copy had drifted badly out of date. The root `README.md` is the single
+source of truth: the package's `prebuild` script copies it in before every
+build (npm cannot publish a symlink, so a real file has to ship in the
+tarball), and a unit test fails CI if the two files ever drift apart.