refactor(mining): extract the Earnings card into mining_earnings.{h,cpp} (audit #10, slice 1)

First incremental slice of decomposing the 2628-line mining_tab.cpp monolith (one giant
RenderMiningTabContent function). The ~636-line "Earnings" card section is moved verbatim into
RenderMiningEarnings(); mining_tab.cpp is now 1992 lines and calls it with the immediate-mode
layout context as parameters (draw list, fonts, scale/spacing, glass spec, pool-mode flag).

Behavior-preserving by construction: the body is byte-identical (the only additions are a
`const bool s_pool_mode = poolMode` alias and a local scratch `buf` so the moved code keeps its
original identifiers). The earnings-filter static moved with the card it belongs to. The
compiler surfaced every enclosing dependency, which became explicit parameters.

Verified: full-node + Windows + lite build, tests, hygiene, clean smoke start. Pending hands-on
visual check of the Earnings card before extracting the next section.

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

src/ui/windows/mining_earnings.h

@@ -0,0 +1,26 @@
+// DragonX Wallet - ImGui Edition
+// Copyright 2024-2026 The Hush Developers
+// Released under the GPLv3
+
+#pragma once
+
+#include "../../data/wallet_state.h"
+#include "../material/draw_helpers.h"  // GlassPanelSpec
+#include "imgui.h"
+
+namespace dragonx {
+class App;
+namespace ui {
+
+// Renders the mining "Earnings" card (Today | Yesterday | All Time | Est. Daily). Extracted
+// verbatim from the monolithic mining tab; the immediate-mode layout context (draw list, fonts,
+// scale/spacing, the glass-panel spec, and the parent's pool-mode flag) is passed in so the
+// rendering flows in sequence exactly as before.
+void RenderMiningEarnings(App* app, const WalletState& state, const MiningInfo& mining,
+                          ImDrawList* dl, ImFont* capFont, ImFont* sub1, ImFont* ovFont,
+                          float dp, float vs, float gap, float pad, bool isMiningActive,
+                          bool poolMode, float availWidth,
+                          const material::GlassPanelSpec& glassSpec, float sHdr, float gapOver);
+
+} // namespace ui
+} // namespace dragonx