feat(ui): in-app FAQ, DPI-scaling audit fixes, mining/stratum polish + localize strings

Bundles the session's UI work (the touched files carry several of these
changes together, so they are committed as one coherent UI batch):

- FAQ: new RenderFaqDialog + data-driven faq_content, opened from a
  status-bar "?" (and the Windows title bar), styled like the Wallets
  modal with search, Wallet/Daemon tabs, and smooth scroll.
- DPI/font-scale audit: multiply hand-drawn absolute geometry by
  Layout::dpiScale() across ~30 files so nothing renders native-size at
  HiDPI / font_scale 1.5 (verified with a full sweep at 1.5x).
- Mining: chart now fills the horizontal space; thread stepper +/- buttons
  match the input-box height; move the stratum-host toggle into
  Node & Security (v1.3.0+).
- Settings: fix the auto-shield status text overlapping the grid.
- Sidebar: drop the peer-count badge on the Network button.
- i18n: wrap 193 hardcoded literals with TR() (keys/translations added in
  the preceding i18n commit), so the security/PIN/lock flow, seed-backup
  wizard, and witness-rebuild dialog localize.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app.h

@@ -462,6 +462,7 @@ public:
         return 0;
     }
     void showAboutDialog() { show_about_ = true; }
+    void showFaqDialog() { show_faq_ = true; }
     
     // Legacy tab compat — maps int to NavPage
     void setCurrentTab(int tab);
@@ -800,6 +801,7 @@ private:
     // balance poll discards per-note data). Mirrors chat_fast_scan_in_flight_.
     bool          chat_note_scan_in_flight_ = false;
     double        chat_note_scan_last_ = 0.0;         // ImGui time of the last note scan (rate limit)
+    double        chat_note_scan_ms_   = 0.0;         // measured cost of the last note scan (adaptive back-off)
     // Most-recent chain tip, cached across refreshes: a lite refresh model that carries spendableOutputs
     // may NOT carry sync status that same cycle (tolerated partial refresh), so verifiedSelfNoteCount reads
     // this cache rather than requiring the current model to have both — else the budget flickers to 0.
@@ -809,6 +811,9 @@ private:
     // Coordinator helpers (both variants unless noted; see app_network.cpp).
     void refreshChatNoteBudget(const wallet::LiteWalletAppRefreshModel& model);  // lite: recompute caches on a fresh model
     void refreshChatNoteBudgetNode();             // full node: rate-limited z_listunspent worker scan
+    // Feeds the SAME chat send-budget from an already-collected z_listunspent (the address refresh),
+    // so the dedicated scan above is skipped while the address refresh is active (dedup — see #3).
+    void updateChatNoteBudgetFromUnspent(const std::vector<services::NetworkRefreshService::UnspentNoteLite>& unspentNotes);
     void pumpChatNoteBuffer();                     // per-frame: drain the queue / build the buffer
     int  verifiedSelfNoteCount(const wallet::LiteWalletAppRefreshModel& model);   // lite
     int  pipelineSelfNoteCount(const wallet::LiteWalletAppRefreshModel& model);   // lite
@@ -877,6 +882,8 @@ private:
     void fastScanChatMemos();
     bool chat_fast_scan_in_flight_ = false;   // guard against overlapping fast-scan RPCs
     float chat_fast_scan_accum_ = 0.0f;       // seconds since the last fast-scan (dedicated ~2.5s poll)
+    double chat_fast_scan_last_ = 0.0;        // ImGui time of the last 0-conf fast scan (adaptive back-off)
+    double chat_fast_scan_ms_   = 0.0;        // measured cost of the last fast scan (z_listreceivedbyaddress)
     bool font_rebuild_requested_ = false;     // set by requestFontRebuild(); consumed in preFrame()
     // Lite first-run welcome prompt: dismissed for the session once the user picks an action.
     bool lite_firstrun_dismissed_ = false;
@@ -1028,6 +1035,7 @@ private:
     bool show_demo_window_ = false;
     bool show_settings_ = false;
     bool show_about_ = false;
+    bool show_faq_ = false;
     bool show_import_key_ = false;
     bool show_export_key_ = false;
     bool show_backup_ = false;
@@ -1143,6 +1151,14 @@ private:
     std::time_t sync_settle_until_ = 0;    // hold the sync-throttle until this wall-clock time (0 = not settling)
     double last_balance_scan_ms_ = 0.0;    // measured cost of the last z_gettotalbalance scan
     bool force_balance_refresh_ = false;   // a wallet mutation forces the next balance poll through the throttle
+    // Same adaptive back-off applied to the other two O(mapWallet) scans that hold the daemon's cs_main:
+    // the address scan (z_listunspent) and the history scan (z_listreceivedbyaddress). Without this, a
+    // large shielded wallet re-scans them every tab cadence (~seconds each), saturating cs_main and
+    // starving block connection near the tip (where effectivelySyncing() reads false). See
+    // addressRefreshDue() / txRefreshDue(); only the routine periodic poll is throttled — explicit
+    // refreshes (tab switch, dirty set, in-flight send) call the refresh directly and bypass this.
+    double last_address_scan_ms_ = 0.0;    // measured cost of the last address scan
+    double last_tx_scan_ms_ = 0.0;         // measured cost of the last history scan
     // Auto-clear for secrets copied to the clipboard. Only a hash of the copied secret is kept.
     std::uint64_t clipboard_secret_hash_ = 0;
     double clipboard_clear_deadline_ = 0.0;
@@ -1498,6 +1514,11 @@ private:
     void applyRefreshPolicy(ui::NavPage page);
     bool effectivelySyncing() const;   // syncing, or within the post-sync settle window (hysteresis)
     bool balanceRefreshDue() const;    // adaptive: enough time elapsed given the last balance-scan cost?
+    bool addressRefreshDue() const;    // same adaptive back-off for the address scan (z_listunspent)
+    bool txRefreshDue() const;         // same adaptive back-off for the history scan (z_listreceivedbyaddress)
+    // Shared duty-cycle rule: a scan may resume only once (lastScanMs / kScanDutyCycle) has elapsed since
+    // lastUpdate, so any single O(mapWallet) scan can occupy at most ~kScanDutyCycle of wall-clock.
+    bool scanRefreshDue(std::int64_t lastUpdate, double lastScanMs) const;
     bool currentPageNeedsWalletDataRefresh() const;
     bool shouldRunWalletTransactionRefresh() const;
     bool shouldRefreshTransactions() const;