Product pivot: defer Home Assistant; provider-based server architecture (Nextcloud default)

ISOLATE (nothing deleted):
- moved HA module (ha/, ui/devices/, HA client tests), e2e scripts, and HA
  docs under deferred/home-assistant/ with a README explaining status + how
  to revive; complete snapshot preserved on branch deferred/home-assistant

REMOVE FROM ACTIVE PRODUCT:
- HomeScreen: Devices card + route gone; MainActivity nav updated
- ShonarApplication: haRepository removed
- BuiltInSettings: Home Assistant category/settings removed from defaults
- SettingsManagerTest: secret tests rewritten around a user-created
  SECRET-type setting (no built-in secret ships)
- Manifest + URL-validation test fixture wording neutralized
- README/ROADMAP: HA marked deferred with pointer to preserved branch

ADD (design, per product direction):
- docs/server-providers.md: ShonarProvider interface, Room data model,
  auth ladder (OIDC/PKCE -> Nextcloud login-flow-v2 -> token paste),
  sync strategy, provider-selection UX (Nextcloud default; Start9/Umbrel
  as platform-probe + explicit service binding, never universal APIs;
  custom SHONAR server; local-only), TLS TOFU pinning policy,
  no-secret-logging rules, provider contract test strategy, phased plan P0-P7

VERIFY: 19 Android unit tests green, APK builds, on-device launch OK
(consent dialog renders; no Devices entry). Backend unchanged (26 tests).

deferred/home-assistant/README.md

@@ -0,0 +1,31 @@
+# DEFERRED: Home Assistant integration
+
+**Status: deferred — not part of SHONAR's initial product scope.**
+
+Home Assistant must not be part of SHONAR's server, storage, authentication,
+onboarding, or default feature set. This directory preserves the work that
+was built (and unit-tested) before the product direction changed, for
+possible future integration. It is excluded from the app build, the default
+settings, the onboarding flow, and the active test plan.
+
+**A complete, compilable copy of this integration (module `com.shonar.ha`,
+Devices screen, e2e scripts, docs) is preserved on git branch
+`deferred/home-assistant`.**
+
+## What is here
+
+| Path | Contents |
+|---|---|
+| `android/src/main/java/com/shonar/ha/` | `HomeAssistantClient` (official REST + WebSocket APIs), `HaRepository`, `HomeAssistantEntity` |
+| `android/src/main/java/com/shonar/ui/devices/` | Devices screen + `HaViewModel` (entity discovery, toggles, live updates) |
+| `android/src/test/java/com/shonar/HomeAssistantClientTest.kt` | 10 MockWebServer tests (401, unreachable, service calls, WS handshake/auth_invalid) |
+| `scripts/ha_e2e_token.sh`, `scripts/ha_e2e_login_flow.sh` | Local-HA e2e auth scripts (official login_flow API, leak-safe) |
+| `docs/home-assistant.md` | Setup/token/troubleshooting guide |
+
+## To revive
+
+1. `git checkout deferred/home-assistant` (or copy these files back).
+2. Re-add the `HA_*` built-in settings and the `home_assistant` category.
+3. Re-wire `ShonarApplication.haRepository`, the `devices` nav route, and the
+   Devices quick-card.
+4. Re-enable the test and run the e2e scripts against a local HA instance.