feat(cardputer-adv): add TCA8418 keyboard and WiFi config UI (#1929)

Add full keyboard support and keyboard-based WiFi configuration for
M5Stack Cardputer Adv:

- TCA8418 I2C keyboard driver with 56-key matrix, interrupt-driven
  key events, and debounce handling
- Keyboard WiFi config UI: scan/select/input SSID and password
  directly on the device without needing a phone
- Volume control (up/down arrows) and brightness control (left/right)
  via keyboard with fine-step adjustment near bounds
- Enter key to toggle chat state
- Display offset and backlight fixes for ST7789V2
- README with flash parameters and hardware specs

Co-authored-by: bot <bot@localhost>

main/boards/m5stack-cardputer-adv/wifi_config_ui.h

@@ -0,0 +1,133 @@
+#ifndef WIFI_CONFIG_UI_H
+#define WIFI_CONFIG_UI_H
+
+#include "tca8418_keyboard.h"
+#include "display/lcd_display.h"
+#include <string>
+#include <vector>
+#include <functional>
+
+// WiFi scan result structure
+struct WifiScanResult {
+    std::string ssid;
+    int8_t rssi;
+    bool is_encrypted;
+};
+
+// WiFi configuration UI state machine
+enum class WifiConfigState {
+    Scanning,       // Scanning for WiFi networks
+    SelectWifi,     // Selecting from WiFi list
+    InputPassword,  // Entering password for selected WiFi
+    InputSsid,      // Manual SSID input
+    InputManualPwd, // Manual password input (after SSID)
+    SavedList,      // Viewing saved WiFi list
+    Connecting,     // Connecting to WiFi
+    Success,        // Connection successful
+    Failed          // Connection failed
+};
+
+// Result of WiFi configuration
+enum class WifiConfigResult {
+    None,           // Still in progress
+    Connected,      // Successfully connected
+    Cancelled       // User cancelled
+};
+
+class WifiConfigUI {
+public:
+    using ConnectCallback = std::function<void(const std::string& ssid, const std::string& password)>;
+
+    WifiConfigUI(LcdDisplay* display);
+    ~WifiConfigUI();
+
+    // Start the WiFi configuration UI
+    void Start();
+
+    // Start directly with saved WiFi list
+    void StartWithSavedList();
+
+    // Handle keyboard events, returns result
+    WifiConfigResult HandleKeyEvent(const KeyEvent& event);
+
+    // Set callback for when connection should be attempted
+    void SetConnectCallback(ConnectCallback callback) { connect_callback_ = callback; }
+
+    // Notify connection result
+    void OnConnectResult(bool success);
+
+    // Check if UI is active
+    bool IsActive() const { return is_active_; }
+
+    // Update cursor blink state (call periodically from main loop)
+    void UpdateCursor();
+
+private:
+    LcdDisplay* display_;
+    WifiConfigState state_;
+    bool is_active_;
+    ConnectCallback connect_callback_;
+
+    // WiFi scan results
+    std::vector<WifiScanResult> scan_results_;
+    int selected_index_;
+    int scroll_offset_;
+
+    // Saved WiFi list
+    std::vector<std::pair<std::string, std::string>> saved_wifi_list_;
+    int saved_selected_index_;
+    int saved_scroll_offset_;
+
+    // Input buffers
+    std::string input_ssid_;
+    std::string input_password_;
+    std::string selected_ssid_;
+    bool input_focus_on_password_;  // For manual input: true = password field, false = ssid field
+
+    // Cursor blinking
+    bool cursor_visible_;
+    uint32_t last_cursor_toggle_;
+    static constexpr uint32_t CURSOR_BLINK_MS = 500;
+
+    // Display constants
+    static constexpr int MAX_VISIBLE_ITEMS = 4;
+    static constexpr int MAX_INPUT_LENGTH = 64;
+
+    // State handlers
+    void StartScanning();
+    void ShowScanResults();
+    void ShowPasswordInput();
+    void ShowManualInput();
+    void ShowSavedList();
+    void ShowConnecting();
+    void ShowSuccess();
+    void ShowFailed();
+
+    // Redraw functions (don't reset state/input)
+    void RedrawPasswordInput();
+    void RedrawManualInput();
+
+    // Input handlers
+    void HandleScanningKey(const KeyEvent& event);
+    void HandleSelectWifiKey(const KeyEvent& event);
+    void HandlePasswordInputKey(const KeyEvent& event);
+    void HandleManualInputKey(const KeyEvent& event);
+    void HandleSavedListKey(const KeyEvent& event);
+    void HandleConnectingKey(const KeyEvent& event);
+    void HandleResultKey(const KeyEvent& event);
+
+    // Helper functions
+    void DrawHeader(const char* title);
+    void DrawFooter(const char* hint);
+    void DrawInputField(const char* label, const std::string& value, bool is_password, bool is_active);
+    void DrawWifiList(const std::vector<WifiScanResult>& list, int selected, int scroll_offset);
+    void DrawSavedWifiList();
+    std::string GetSignalBars(int8_t rssi);
+    void LoadSavedWifiList();
+    void SaveWifiCredentials(const std::string& ssid, const std::string& password);
+    void DeleteSavedWifi(int index);
+    void DoWifiScan();
+    void AttemptConnection();
+};
+
+#endif // WIFI_CONFIG_UI_H