chore(repo): establish isolated mobile repository and upstream audit

docs/upstream-audit.md

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+# Upstream source audit
+
+Inspected 2026-10-20: https://github.com/ulsklyc/yuvomi
+revision `10bfef7686ed7303b4c74c7fcc55a5eb16356c9d`, package version `2.78.0`.
+Source was cloned outside this repository; no upstream files were modified.
+
+Read README, CONTRIBUTING (including AI disclosure), SECURITY, DESIGN, package
+manifest, server/index.js, server/auth.js, public/sw.js, sw-register.js and
+notification settings. Reviewed the latest 100 open issues/PRs via GitHub API;
+that sample is not an exhaustive review of all historical reports.
+
+Findings:
+
+- Frontend has no framework/build step; native projects remain separate.
+- Public `/api/v1/version` exposes `app_name`, `setup_required`,
+  `password_reset_enabled`, **not** a release number before authentication.
+- `/api/v1/auth/oidc/config` exposes enabled/password-login flags.
+- Sessions are HttpOnly, SameSite=Lax, persistent cookies. Operators must set
+  `SESSION_SECURE=true` behind TLS. Native code must not replace auth or CSRF.
+- Username/password, TOTP/recovery codes, reset and logout are web features.
+- OIDC stores state, nonce and PKCE in the initiating browser's server session,
+  and returns to the configured server callback. There is no mobile callback,
+  one-time session exchange, or universal-link association protocol.
+- Root-relative API, assets, redirects, service-worker registration and cookie
+  path mean subpaths cannot be promised. Use a dedicated hostname instead.
+- Service worker has versioned shell caches and allow-listed read-only API
+  caching; mutations and authentication remain network-only. No offline editing.
+- Web Push is not native push. Optional upstream ntfy/Gotify/webhook channels
+  provide self-hosted alternatives through their own clients.
+- Upstream uses violet `#6C3AED`, warm grouped background `#F5F3ED`, and native
+  system fonts. Native screens follow these tokens without changing web design.
+
+Compatibility probing is structural, not cryptographic identification: any server
+can imitate the public endpoints. Users must trust the URL they enter. Exact release
+compatibility needs authenticated integration testing; no version range is inferred.