refactor(mining): extract the Mode toggle into mining_mode_toggle.{h,cpp} (audit #10, slice 4)

Final slice of decomposing mining_tab.cpp. The ~529-line "Mode toggle" section (SOLO | POOL
segmented control + pool URL/worker inputs) is moved verbatim into RenderMiningModeToggle().
mining_tab.cpp is now 311 lines (was 2628) — just the tab dispatch, thread-sync glue, benchmark
advance, section-budget setup, and four card calls.

State the toggle mutates is passed BY REFERENCE so behaviour is identical: the pool-mode flag,
the settings-dirty flag, and the pool URL / worker char[256] buffers (the text inputs write into
them) — passed as char(&)[256] references and named with their original identifiers so the body
stays byte-identical.

Verified: full-node + Windows + lite build, tests, hygiene. Audit #10 complete: the 2628-line
monolith is now five focused files (earnings, stats, controls, mode-toggle + the 311-line shell).

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

src/ui/windows/mining_mode_toggle.h

@@ -0,0 +1,25 @@
+// DragonX Wallet - ImGui Edition
+// Copyright 2024-2026 The Hush Developers
+// Released under the GPLv3
+
+#pragma once
+
+#include "../../data/wallet_state.h"
+#include "imgui.h"
+
+namespace dragonx {
+class App;
+namespace ui {
+
+// Renders the mining "Mode toggle" (SOLO | POOL segmented control + pool URL/worker inputs).
+// Extracted verbatim from the monolithic mining tab. The state it mutates is passed BY REFERENCE:
+// the pool-mode flag, the pool URL / worker text buffers, and the settings-dirty flag (named with
+// their original identifiers so the moved body is byte-identical).
+void RenderMiningModeToggle(App* app, const WalletState& state, const MiningInfo& mining,
+                            ImDrawList* dl, ImFont* capFont, ImFont* ovFont,
+                            float dp, float hs, float gap, float availWidth,
+                            bool& s_pool_mode, char (&s_pool_url)[256], char (&s_pool_worker)[256],
+                            bool& s_pool_settings_dirty);
+
+} // namespace ui
+} // namespace dragonx