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

docs/library-decisions/2026-05-14-tailwind-merge.md

@@ -0,0 +1,69 @@
+---
+package: tailwind-merge
+version: "^3.0.0"
+tier: core
+decision: approved
+date: 2026-05-14
+deciders: [scaffolded]
+adr: null
+filter-results:
+  license: MIT
+  types: native
+  maintenance: active
+  boundary-fit: pass
+  shadow-check: pass
+  eu-residency: n/a
+  cve-scan: clean
+  named-consumer: pass
+  socketRisk: clean
+verification-commands:
+  - pnpm audit --audit-level=moderate
+  - npm view tailwind-merge license
+accepted-cves: []
+---
+
+## Filter: license
+
+MIT — on the workspace allowlist.
+
+## Filter: types
+
+Ships first-party TypeScript types in its distribution.
+
+## Filter: maintenance
+
+Active. Maintained by dcastil; v3 is the current stable major.
+
+## Filter: boundary-fit
+
+Core UI package. `tailwind-merge` deduplicates conflicting Tailwind classes; appropriate for `core-ui`. No boundary rule violation.
+
+## Filter: shadow-check
+
+No competing Tailwind class-merging utility in the workspace. No shadow.
+
+## Filter: eu-residency
+
+Pure compute; no network calls or vendor data transmission. n/a.
+
+## Filter: cve-scan
+
+No advisories at adoption time.
+
+## Filter: named-consumer
+
+`core-ui` uses `tailwind-merge` in the `cn()` utility (combined with `clsx`) to resolve conflicting Tailwind class names at runtime.
+
+## Prompt: replaces
+
+Nothing — this is the initial UI scaffold.
+
+## Prompt: migration-cost-out
+
+Mechanical: replace `twMerge()` calls in the `cn()` utility; update any call sites. Narrow API surface.
+
+## Prompt: alternatives-considered
+
+1. **Custom deduplication** — error-prone; Tailwind has hundreds of class groups that change each version.
+2. **tw-join** — does not merge conflicts; only concatenates.
+   `tailwind-merge` is the de-facto standard for conflict-free Tailwind class composition.