Create a Devtoberfest Homepage #397

feat(db): DevtoberfestConfig + EventRegistrations entities

feat(admin): DevtoberfestConfig + EventRegistrations AdminService pro…

docs(plan): fix Devtoberfest singleton UUID — 37 chars → 36

feat(srv): /api/devtoberfest/status — event-missing 503 path

feat(srv): /api/devtoberfest/status — resolve joined state per caller

docs(plan): wire cds.middlewares.context/auth in route register() blocks

feat(srv): /api/devtoberfest/terms — public T&C body + version

docs(plan): use resolveUserSapId() in /me + /join handlers

feat(srv): /api/devtoberfest/me — caller's registration state

feat(srv): POST /api/devtoberfest/join — happy path

test(srv): /api/devtoberfest/join — error-branch coverage

feat(approuter): /devtoberfest + /api/devtoberfest/* routes

feat(hugo): /devtoberfest/ page scaffold + placeholder SVG assets

feat(hugo-apps): Devtoberfest homepage Vue island

feat(hugo-apps): T&C dialog + JOIN flow

feat(admin): Devtoberfest admin tile — Config + Registrations views

feat(admin-shell): wire Devtoberfest tile into navigation

feat(annotations): DevtoberfestConfig + EventRegistrations labels

test(hybrid): Devtoberfest join — real HANA round-trip

test(smoke): Devtoberfest endpoints — deployed DEV