fix(diagnostics): address adversarial review of the QoL UI (popup, staleness, DPI, i18n)

Follow-up to the node-banner / staleness-badge / alert-history features — a 5-dimension
finder->verify review surfaced 4 real issues (the ImGui-stack-balance finder found none):

- Alert popup grew off the right edge: pivot (0,1) pinned the panel's LEFT edge at the
  bell, which sits near the window's right edge, so a 320px panel overflowed rightward
  (an explicit SetNextWindowPos pivot skips ImGui's on-screen clamp). Anchor the
  bottom-RIGHT corner at the bell instead (pivot (1,1) at bellMax.x) so it grows left.

- Staleness badge could flash red on reconnect: WalletState::clear() reset everything
  except the four last_*_update stamps, so the pre-outage timestamp survived and the
  badge briefly showed "Updated Nm ago" the same frame the node banner cleared. Zero the
  stamps in clear() (all readers treat 0 as "never"; app_network.cpp:1473 guards != 0).

- Banner min-height floor wasn't DPI-scaled: std::max(minH, baseH*vScale()) now uses
  minH * dpiScale() so both operands are in scaled px.

- New i18n keys weren't in res/lang/: back-filled all 16 diagnostics/QoL keys into the 8
  language files, additively (128 insertions, 0 deletions). zh/ja/ko reworded around 2
  glyphs missing from the CJK subset and hard-asserted tofu-free against the subset font.

Build-clean both variants; ctest 1/1.

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

src/data/wallet_state.h

@@ -339,6 +339,11 @@ struct WalletState {
         // stops), so leaving the previous wallet's hashrate/blocks would show stale mining stats.
         mining = MiningInfo{};
         pool_mining = PoolMiningState{};
+        // After a disconnect / wallet switch nothing is freshly known, so drop the "last successful
+        // refresh" stamps. Otherwise the pre-teardown time survives and, on reconnect, the staleness
+        // badge (and any "updated X ago" reader) briefly reports it as current until the first refresh
+        // re-stamps it. All readers treat 0 as "never" (formatTimeAgoShort/timeAgo return "").
+        last_balance_update = last_tx_update = last_peer_update = last_mining_update = 0;
     }
     
     // Rebuild combined addresses list from z/t lists