Documenting folders architecture (#66)

* documented new folder layout that respects chess layers

* renaming files to suit the latest needs

Author: Hardcode3

include/bitbishop/attacks/attackers_to.hpp

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+# About the `attacks/` directory
+
+## The core rule
+
+Lookups = immutable, compile-time geometry
+
+Attacks = runtime logic that depends on board state
+
+## What exactly goes into `attacks/`
+
+### Definition
+
+attacks/ contains functions that:
+
+- consume lookup tables
+- take runtime state (occupied)
+- compute attack bitboards dynamically
+
+### Examples (good)
+
+```cpp
+// attacks/bishop_attacks.cpp
+Bitboard bishop_attacks(Square from, Bitboard occupied);
+
+// attacks/attackers_to.cpp
+Bitboard attackers_to(Square sq, const Board&, Color);
+```
+
+### Examples (bad — belongs elsewhere)
+
+```cpp
+constexpr Bitboard KING_ATTACKS[64]; // ❌ data only
+generate_legal_moves(...) // ❌ rules layer
+```

include/bitbishop/attacks/bishop_attacks.hpp

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+# About the `engine/` directory
+
+## The core rule
+
+Engine = decision making
+
+This layer decides which move to play, not which moves are legal.
+
+## What exactly goes into `engine/`
+
+### Definition
+
+engine/ contains logic that:
+
+- searches the game tree
+- evaluates positions
+- selects the best move
+
+This layer may:
+
+- call generate_legal_moves()
+- make/unmake moves on the Board
+- maintain search state
+
+This layer must not:
+
+- implement chess rules
+- generate attacks directly
+- contain UI or protocol code
+
+Typical responsibilities
+
+- search algorithms:
+- Minimax
+- Alpha-Beta
+- MCTS
+- evaluation functions
+- move ordering
+- transposition tables
+- time management (search side)
+
+### Examples (good)
+
+```cpp
+// engine/search.cpp
+Move search_best_move(Board&, SearchLimits);
+
+// engine/eval.cpp
+int evaluate(const Board&);
+```
+
+### Examples (bad — belongs elsewhere)
+
+```cpp
+void generate_legal_rook_moves(...); // ❌ movegen
+constexpr Bitboard ROOK_RAYS[64][4]; // ❌ lookups
+void uci_loop(); // ❌ interface
+```

include/bitbishop/attacks/queen_attacks.hpp

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+# About the `interface/` directory
+
+## The core rule
+
+Interface = communication with the outside world
+
+This layer translates between the engine and humans or GUIs.
+
+## What exactly goes into interface/
+
+### Definition
+
+interface/ contains logic that:
+
+- parses input commands
+- formats output
+- manages clocks and sessions
+- interacts with GUIs or users
+
+This layer may:
+
+- call engine entry points
+- read/write text or UI events
+
+This layer must not:
+
+- implement search logic
+- implement chess rules
+- manipulate bitboards directly
+
+Typical responsibilities
+
+- UCI / CECP protocol handling
+- GUI hooks
+- command parsing
+- time control management
+- logging
+
+### Examples (good)
+
+```cpp
+// interface/uci.cpp
+void uci_loop();
+
+// interface/cli.cpp
+void run_cli();
+```
+
+### Examples (bad — belongs elsewhere)
+
+```cpp
+Bitboard attackers_to(...); // ❌ attacks
+int alpha_beta(...); // ❌ engine
+generate_legal_moves(...); // ❌ movegen
+```