feat(diagnostics): refresh-staleness badge on the Total Balance card (W6-2)

When the wallet is connected but the balance has quietly stopped refreshing — a busy
daemon can fail z_gettotalbalance without dropping the whole connection (only *both*
core RPCs failing 3x triggers a disconnect) — the old number sits on screen while the
node-status banner stays hidden. The Total Balance card now shows a small pill on its
status line ("Updated 2m ago", amber, escalating to red past 3 min) so the stale value
isn't silently trusted; hovering explains it and points at the node connection.

No refresh-path changes: WalletState::last_balance_update is already stamped only on a
successful fetch (network_refresh_service.cpp), so the badge reads it and computes age
against the same std::time clock via util::formatTimeAgoShort. The decision is a pure,
unit-tested helper (ui/staleness_badge.h::evaluateStalenessBadge, 45s/180s thresholds)
gated on connected so it never contradicts the banner.

Closes P2 (5/5). Build-clean; ctest 1/1 (adds testStalenessBadge).

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

docs/wallet-hardening.md

@@ -20,8 +20,8 @@ Status legend: ☐ not started · ◐ in progress · ☑ landed & verified
 | **P0-B** | W2-2/W4-2, W2-4 | Encryption integrity (never silently unencrypted) | ☑ |
 | **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 + node-error-banner ✓, alert-history/staleness ☐ | Diagnostics foundation + QoL bundle | ◐ |
+| **P2**  | W5-1, W5-2, W6-1, W6-3, W6-2 ✓ | Stale state & lite save-failure surfacing | ☑ 5/5 |
+| **F**   | W7-2, W7-3, W7-4 ✓ · QoL: copy-diag + open-log + node-error-banner + staleness-badge ✓, alert-history ☐ | Diagnostics foundation + QoL bundle | ◐ |
 
 ---
 
@@ -112,6 +112,7 @@ Land W7-2 first — it unblocks the rest.
 
 ## Progress log
 
+- **W6-2 / Refresh-staleness badge** — ☑ landed. The Total Balance card now shows a small pill on its status line ("Updated 2m ago", amber → red past 3 min) **only when connected but the balance stopped refreshing** — a busy daemon can fail `z_gettotalbalance` without dropping the whole connection (only *both* core RPCs failing 3× triggers a disconnect), leaving stale numbers on screen while the node-status banner stays hidden. No refresh-path changes were needed: `WalletState::last_balance_update` is already stamped only on a successful fetch (`network_refresh_service.cpp:1187`), so the badge just reads it and computes age against the same `std::time` clock (`util::formatTimeAgoShort`). Decision is a pure, unit-tested helper (`ui/staleness_badge.h::evaluateStalenessBadge`, thresholds 45s/180s) gated on `connected` so it never contradicts the banner; hover shows a "may be out of date — check your node connection" tooltip. Build-clean; `ctest` 1/1 (adds `testStalenessBadge`). **This closes P2 (5/5).**
 - **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):