Data-layer BDD testing infrastructure and steps/frontend → steps/ui rename

- Rename steps/frontend/ to steps/ui/ across all modules and shared
- Add data-layer test harness (mock + real broker modes) with Playwright
- Add inscription data-layer steps (@data scenarios)
- Add test auth setup script and browser debug script
- Update docs (architecture, BDD testing, data-layer testing)
- Add ADR for headless wallet creation decision

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.project/decisions/2026-03-12-1500-headless-wallet-creation.md

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+# Automated Headless Wallet Creation for CI
+
+**Date:** 2026-03-12 15:00
+**Status:** Accepted
+
+## Context
+
+Data-layer BDD tests (`@data` scenarios) require a NextGraph wallet in a persistent Chromium profile. Previously, the first run required manual interaction: a visible browser opened and the user had to create a wallet and close the browser. This blocked CI execution.
+
+## Options Considered
+
+### Option A: Programmatic wallet creation via NG SDK
+Call `ng.wallet_create()` directly from Node/Bun, bypassing the UI entirely.
+
+**Arguments for:**
+- Fastest execution
+- No browser needed for wallet creation
+
+**Arguments against:**
+- `@ng-org/web` is browser-only (WASM + postMessage)
+- Would need to reverse-engineer the registration API at `account.nextgraph.eu`
+- Doesn't test the real auth flow
+
+### Option B: Automate the browser UI flow headlessly
+Use Playwright to drive the same wallet creation UI a real user would use, but in headless mode.
+
+**Arguments for:**
+- Tests the real auth/login feature end-to-end
+- No API reverse-engineering needed
+- Same persistent profile used for subsequent test runs
+- CI-ready with no manual steps
+
+**Arguments against:**
+- Depends on `nextgraph.eu` and `account.nextgraph.eu` being reachable
+- UI changes in NextGraph could break the automation
+- Adds ~27s to first run
+
+## Decision
+
+Option B — automate the browser UI. The wallet creation flow (navigate to `nextgraph.eu` → "Create Wallet" → accept ToS at `account.nextgraph.eu` → fill username/password → submit) is itself a legitimate test of the app's auth feature. The dependency on external services is acceptable since the tests already depend on the broker being reachable.
+
+## Consequences
+
+**Positive:**
+- Tests are fully CI-ready (no human interaction)
+- Auth/login flow is tested as a side effect
+- Single command `bun run test:data` works from a clean state
+
+**Negative:**
+- Requires internet access (nextgraph.eu, account.nextgraph.eu)
+- Fragile to NextGraph UI changes (button text, form IDs)
+
+**Risks:**
+- `account.nextgraph.eu` rate limiting could block CI runs that frequently recreate wallets