rename(phase 1): CapaKraken → Nexus across code, UI, docs, CI

- @capakraken/* → @nexus/* across 12 packages (root + 11 workspaces),
  1551 import lines migrated via codemod
- User-visible brand strings renamed (emails, page titles, PWA
  manifest, mobile header, MFA backup-codes header, tooltips, signin
  page, invite page, weekly digest, install prompt)
- TOTP issuer "CapaKraken" → "Nexus" (existing secrets still valid;
  re-enrollment relabels them in users' authenticator apps)
- Function rename: assertCapaKrakenDbTarget → assertNexusDbTarget
- LocalStorage migration shim in apps/web/src/app/layout.tsx copies
  capakraken_* → nexus_* on first load (guarded by nexus_migrated_v1
  sentinel; runs once per browser, then never again)
- Service-worker cache name capakraken-v2 → nexus-v2 with one-time
  caches.delete('capakraken-v2') from the same shim
- Email-domain fixtures @capakraken.{dev,app} → @nexus.{dev,app} in
  seed data, e2e specs, SMTP default fallback
- Dockerfile.dev / Dockerfile.prod / all .github/workflows/*.yml
  pnpm --filter @capakraken/* → @nexus/*
- README, CLAUDE.md, LEARNINGS.md, all docs/*.md, .env.example,
  tooling/deploy/.env.production.example brand sweep

Phase 1 deliberately leaves untouched (handled in Phase 3 cutover):
- PostgreSQL DB name "capakraken" and POSTGRES_USER "capakraken"
- Volume names capakraken_pgdata etc.
- Compose project name "capakraken" / "capakraken-prod"
- db-target-guard default expectedDatabase
- env-var CAPAKRAKEN_EXPECTED_DB_NAME
- Container DNS names in docker-compose.ci.yml

Quality gates green: pnpm typecheck (7/7), pnpm test:unit (7/7),
pnpm lint (0 errors), check:exports/imports/architecture all pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/import-hardening.md

@@ -12,7 +12,7 @@
 
 ## Server Boundary
 
-The dispo-import reader in [read-workbook.ts](/home/hartmut/Documents/Copilot/capakraken/packages/application/src/use-cases/dispo-import/read-workbook.ts) now enforces:
+The dispo-import reader in [read-workbook.ts](/home/hartmut/Documents/Copilot/nexus/packages/application/src/use-cases/dispo-import/read-workbook.ts) now enforces:
 
 - normalized filesystem paths before reading
 - regular-file checks
@@ -22,11 +22,11 @@ The dispo-import reader in [read-workbook.ts](/home/hartmut/Documents/Copilot/ca
 - a worksheet column limit of `256`
 - `.xlsx`-only parsing through `exceljs` behind a hardened server-side parser boundary
 
-The API entry points in [dispo.ts](/home/hartmut/Documents/Copilot/capakraken/packages/api/src/router/dispo.ts) reject non-`.xlsx` workbook paths before staging or validation begins.
+The API entry points in [dispo.ts](/home/hartmut/Documents/Copilot/nexus/packages/api/src/router/dispo.ts) reject non-`.xlsx` workbook paths before staging or validation begins.
 
 ## Browser Boundary
 
-The browser import helpers in [excel.ts](/home/hartmut/Documents/Copilot/capakraken/apps/web/src/lib/excel.ts) and [skillMatrixParser.ts](/home/hartmut/Documents/Copilot/capakraken/apps/web/src/lib/skillMatrixParser.ts) now enforce:
+The browser import helpers in [excel.ts](/home/hartmut/Documents/Copilot/nexus/apps/web/src/lib/excel.ts) and [skillMatrixParser.ts](/home/hartmut/Documents/Copilot/nexus/apps/web/src/lib/skillMatrixParser.ts) now enforce:
 
 - a hard client-side file size limit of `10 MiB`
 - explicit rejection of legacy `.xls`