Characters: one file per character with a world per difficulty

- CharacterNN.sacredK holds the shared hero and one world per difficulty,
  plus an autosave file; the game works in save\characters\_work
- Load window: one row per character, a difficulty dialog on Laden
  (worlds, newer autosaves, "(neu)" starts a new game with the shared
  hero), Umbenennen, delete moves the character to characters\deleted
- The world keeps its own portals and hero position when the shared hero
  is put on
- K and the Esc menu's "Speichern" save directly (quicksave path)
- One-time migration of the old save rows and exported heroes, after a
  backup
- Startup no longer hangs in the game's foreground loop (0x810af0)
- Text overrides apply to our own text ids too; shared cUI_Button2
  helpers in game/ui/button.h

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/mods/charfile.h

@@ -0,0 +1,82 @@
+#pragma once
+// Character files (docs/characters.md): one file per character with its shared
+// hero and one world per difficulty, plus reading the game's save files.
+
+#include <cstdint>
+#include <optional>
+#include <string>
+#include <vector>
+
+#include <nlohmann/json.hpp>
+
+namespace mods::characters {
+
+using Bytes = std::vector<uint8_t>;
+
+// Bronze, Silber, Gold, Platin, Niob (g_gameLevel 0..4).
+constexpr int kDifficultyCount = 5;
+
+// What the game's save files (GAME.PAK "AMS", hero files .pax "AMH") say about
+// their hero: header 0x100 bytes, then a table of 64 chunks {type, offset,
+// size}; chunk 0xc3 is the hero header.
+struct SaveInfo {
+    std::wstring name;                 // hero header +8, UTF-16
+    uint32_t heroClass = 0;            // hero header +4: 1 Seraphim .. 9 Daemonin
+    uint32_t level = 0;                // hero header +0
+    bool world = false;                // a save game (AMS), not a hero file
+    int difficulty = 0;                // AMS header +0x84 (g_gameLevel)
+    uint32_t mode = 0;                 // AMS header +0x24: 2 normal, 3 hardcore
+    bool multiplayer = false;          // AMS header +0x2c
+    uint64_t savedAt = 0;              // AMS header +0x5c SYSTEMTIME, as FILETIME
+};
+std::optional<SaveInfo> ReadSaveInfo(const Bytes& file);
+
+// Writes `name` as the hero's name (hero header +8, 0x40 UTF-16 characters
+// with the terminator), the only place the name is stored; false if the file
+// has no hero header or the name is empty or too long.
+constexpr size_t kHeroNameMaxChars = 63;
+bool SetHeroName(Bytes& file, const std::wstring& name);
+
+// A small save game the game's load window can list: `world`'s header with its
+// date, its thumbnail and world time, and `description` (ANSI, up to 63
+// characters) as the save's name.
+Bytes BuildPreview(const Bytes& world, const std::string& description);
+
+// Reading and writing whole files (paths in the game's code page).
+std::optional<Bytes> ReadFile(const std::string& path);
+bool WriteFileReplacing(const std::string& path, const Bytes& bytes);
+
+// A character file: named sections ("meta" JSON, "hero" .pax, "world<d>"
+// GAME.PAK). Sections are read from disk on demand; Save writes all of them
+// to a temporary file and replaces the old one.
+class CharacterFile {
+public:
+    explicit CharacterFile(std::string path) : path_(std::move(path)) {}
+
+    // Reads the section table and the meta; false if the file is missing or
+    // not a character file.
+    bool Open();
+
+    const std::string& Path() const { return path_; }
+    bool Has(const std::string& section) const;
+    std::optional<Bytes> Read(const std::string& section) const;
+    void Set(const std::string& section, Bytes bytes);
+    void Remove(const std::string& section);
+    bool Save();
+
+    nlohmann::json meta = nlohmann::json::object();
+
+private:
+    struct Section {
+        std::string name;
+        uint32_t offset = 0;  // in the file; unused once `data` is set
+        uint32_t size = 0;
+        std::optional<Bytes> data;  // set or changed since Open
+    };
+    std::string path_;
+    std::vector<Section> sections_;
+};
+
+std::string WorldSection(int difficulty);
+
+} // namespace mods::characters