chore(template): clean-slate template snapshot from bb4a0c7

Curated, product-agnostic snapshot of the post-story-04 tree: demo
content deleted, auth-only reference feature, web-next shell, all gates
green. Product-specific docs, ADRs 027-029, PRDs/epics/archive, editor
library traces, and product naming are curated out; generic template
repairs (coverage provider devDeps, root test:coverage script, live
lint fixes, root-only release-please) are kept. See TEMPLATE.md for
provenance, curation list, and usage.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK

turbo/generators/templates/feature/stryker.config.json.hbs

@@ -0,0 +1,5 @@
+{
+  "$schema": "../../node_modules/@stryker-mutator/core/schema/stryker-schema.json",
+  "_comment": "{{kebabCase name}} feature mutation testing config. Extends @repo/core-testing/stryker.base.json (ADR-020 L3). Run with `pnpm mutate --filter @repo/{{kebabCase name}}`.",
+  "extends": "@repo/core-testing/stryker.base.json"
+}