Add BT1035 pairing and station presets (fw 0.7.0).

Expose discoverable mode and A2DP control over REST, add persisted
DAB/FM preset list with web UI, and document gaps in docs/TODO.md.

Co-authored-by: Cursor <cursoragent@cursor.com>

Software/components/core/src/PresetSlot.cpp

@@ -0,0 +1,36 @@
+/**
+ * @file    PresetSlot.cpp
+ * @brief   PresetSlot implementation.
+ *
+ * DigiRadio firmware — https://github.com/manvalan/DigiRadio
+ *
+ * Copyright 2026 Michele Bigi
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * @author  Michele Bigi
+ * @date    2026-07-06
+ */
+
+#include "core/PresetSlot.hpp"
+
+namespace core {
+
+std::expected<PresetSlot, ParseError> PresetSlot::tryFrom(unsigned slot) noexcept
+{
+    if (slot < 1U || slot > kMaxSlot) {
+        return std::unexpected(ParseError::MissingField);
+    }
+    return PresetSlot(static_cast<std::uint8_t>(slot));
+}
+
+PresetSlot::PresetSlot(std::uint8_t slot) noexcept
+    : slot_(slot)
+{
+}
+
+std::uint8_t PresetSlot::value() const noexcept
+{
+    return slot_;
+}
+
+} // namespace core