feat(diagnostics): persistent node/RPC error banner at top of content (Foundation QoL)

A persistent horizontal strip now appears at the top of the content column whenever the
wallet can't reach its node — unlike the transient toasts it stays up for as long as the
fault persists, so an offline wallet is never silently mistaken for a working one.

The show/severity/action decision is a pure, unit-tested function
(ui/node_status_banner.h::evaluateNodeStatusBanner) fed a state snapshot by the new
App::renderNodeStatusBanner(). Three cases:
  - full-node offline        -> amber, "Reconnect"    (App::tryConnect)
  - embedded daemon crashed
    & auto-restart gave up    -> red,   "Restart node" (App::restartDaemon)
  - lite wallet open failed   -> red,   message-only

Suppressed during the wizard / wallet-switch / daemon-restart / screenshot-sweep / shutdown,
and while an expected startup phase (warmup / init / connect-in-progress) already owns the
screen. Banner height lives in res/themes/ui.toml (banners.node-status); colours come from the
material semantic palette; the detail text is ellipsis-clipped so it can't push the action
button off-screen. Drawn before the content edge-fade vertex capture so it stays fully opaque.

New i18n keys (node_banner_*). Build-clean both variants; ctest 1/1 (adds testNodeStatusBanner).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/wallet-hardening.md

@@ -21,7 +21,7 @@ Status legend: ☐ not started · ◐ in progress · ☑ landed & verified
 | **P1-A** | W3-1, W3-2, W3-4 ✓ · W3-3 ⚑ | Migrate-to-seed correctness (fund-adjacent) | ◐ 3/4 |
 | **P1-B** | W1-1, W1-2, W1-3, W1-4 ✓ + startup guard | Missing/wrong wallet-file safety | ☑ |
 | **P2**  | W5-1, W5-2, W6-1, W6-3 ✓ · W6-2 ☐ | Stale state & lite save-failure surfacing | ◐ 4/5 |
-| **F**   | W7-2, W7-3, W7-4 ✓ · QoL: copy-diag + open-log ✓, alert-history/error-banner/staleness ☐ | Diagnostics foundation + QoL bundle | ◐ |
+| **F**   | W7-2, W7-3, W7-4 ✓ · QoL: copy-diag + open-log + node-error-banner ✓, alert-history/staleness ☐ | Diagnostics foundation + QoL bundle | ◐ |
 
 ---
 
@@ -112,6 +112,7 @@ Land W7-2 first — it unblocks the rest.
 
 ## Progress log
 
+- **Foundation QoL / Persistent node-status banner** — ☑ landed. A persistent horizontal strip now sits at the top of the content column whenever the wallet can't reach its node — distinct from the transient toasts, so an offline wallet is never silently mistaken for a working one. The show/severity/action decision is a pure function (`ui/node_status_banner.h` → `evaluateNodeStatusBanner`, unit-tested) fed a state snapshot by `App::renderNodeStatusBanner()`. Three cases: **full-node offline** (amber, "Reconnect" → `tryConnect`), **embedded daemon crashed & auto-restart gave up** (red, "Restart node" → `restartDaemon`), **lite wallet failed to open** (red, message-only). Suppressed during the wizard / wallet-switch / daemon-restart / screenshot-sweep / shutdown, and while an expected startup phase (warmup/init/connect-in-progress) already owns the screen. Height in `res/themes/ui.toml` (`banners.node-status`); colours from the material semantic palette; detail text ellipsis-clipped so it can't shove the action button off-screen. Build-clean; `ctest` 1/1 (added `testNodeStatusBanner`). **Remaining QoL:** persistent alert history, and the W6-2 refresh-staleness badge.
 - **Foundation QoL / "Copy diagnostics" + "Open log folder"** — ☑ landed: Settings (logging section) now has two actions. **Open log folder** opens the config dir (`Platform::openFolder`) so users can actually find `dragonx-debug.log`/`dragonx-crash.log`. **Copy diagnostics** copies a plaintext support snapshot to the clipboard via the new `App::buildDiagnosticsReport()` — version, build variant, platform, connection status, active wallet path + existence + size, encryption/lock state, sync heights, daemon status/running/crash-count/lastError (full-node), and the log paths. No secrets. Build-clean; `ctest` 1/1. **Remaining QoL:** persistent alert history, a daemon/RPC error banner, and the W6-2 refresh-staleness badge.
 - **Foundation / W7-2 · W7-3 · W7-4 (diagnostics infrastructure)** — ☑ landed (answers the original "easier to diagnose" ask — the logging/crash foundation now actually works):
   - **W7-2 (Med, keystone):** the app-level `Logger` file sink was never initialized, so `LOG`/`LOGF`/`VERBOSE_LOGF` went nowhere and `dragonx-debug.log` didn't exist on Linux/macOS at all. `main()` now calls `Logger::init(<config>/dragonx-debug.log)` on all platforms. Also fixed a **latent deadlock** this exposed: `init()` wrote its banner via `write()`, which re-locks the non-recursive `mutex_` it already holds — now written directly. On Windows the raw stdout/stderr `freopen` was moved to a separate `dragonx-stdout.log` so the two writers don't contend. New `testLoggerFileSink` (also a deadlock guard — it would hang if that regressed).