docs(skills): repoint drizzle index guidance at the collapsed root

Rebase fallout: main's `stash-indexing` skill (#773) and the indexing
section it added to `stash-drizzle` both import `encryptedIndexes` from
`@cipherstash/stack-drizzle/v3`, a subpath this branch removes when it
collapses `./v3` into the package root. Both files ship to customer repos,
so the stale specifier would not resolve in a freshly-initialised project.

Caught by `scripts/__tests__/no-removed-drizzle-surface.test.mjs`, the
guard this branch added for exactly this drift.

Author: tobyhede

skills/stash-drizzle/SKILL.md

@@ -377,7 +377,7 @@ if (!decrypted.failure) {
 Drizzle emits the encrypted query operators, but **no index DDL** — without functional indexes over the `eql_v3.*` term extractors, every encrypted predicate sequential-scans. `encryptedIndexes` derives the recommended indexes for every encrypted column in the table from its domain, so a schema column can't be forgotten:
 
 ```typescript
-import { encryptedIndexes, types } from "@cipherstash/stack-drizzle/v3"
+import { encryptedIndexes, types } from "@cipherstash/stack-drizzle"
 import { integer, pgTable } from "drizzle-orm/pg-core"
 
 export const users = pgTable(

skills/stash-indexing/SKILL.md

@@ -254,7 +254,7 @@ Index not being used:
 
 **The integrations emit the query operators for you — none applies index DDL on its own. Making sure these indexes exist is always your job.** This skill is the general model — recipes, engagement rules, verification. How to apply it in a specific integration lives in that integration's skill:
 
-- **Drizzle** — `encryptedIndexes(t)` from `@cipherstash/stack-drizzle/v3` derives the recommended indexes for every encrypted column in the table, or declare individual expression indexes in the schema DSL. See `stash-drizzle` § Indexing Encrypted Columns.
+- **Drizzle** — `encryptedIndexes(t)` from `@cipherstash/stack-drizzle` derives the recommended indexes for every encrypted column in the table, or declare individual expression indexes in the schema DSL. See `stash-drizzle` § Indexing Encrypted Columns.
 - **Prisma Next** — Prisma's schema language cannot express functional indexes; the DDL goes in a migration in the adapter's flow. See `stash-prisma-next`.
 - **Supabase** — a `supabase/migrations/` file; no superuser needed (see above). See `stash-supabase`.
 - **Raw SQL / plain PostgreSQL** — the recipes in this skill, in whatever migration tool owns the schema. Never ad-hoc in production.