feat: new type of non-violent 'combat': work

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+# Bank System
+
+The bank system allows players to store items permanently, freeing up inventory space.
+
+## Objects
+
+### bank_booth
+
+A bank terminal that players can interact with. Has no special behavior — the `bank` command checks for any `bank_booth` object in the room.
+
+```yaml
+id: bank_booth
+name: bank booth
+color: "226"
+description: "..."
+inroom_description: "A bank booth is set into the wall."
+```
+
+To place a bank booth in a room, add it to the room's `objects:` list:
+
+```yaml
+objects:
+  - id: bank_booth
+```
+
+## Commands
+
+| Command | Description |
+|---------|-------------|
+| `bank` | Opens bank interface (requires bank booth in room) |
+| `use bank` | Same as `bank` |
+
+### Bank Interface Commands
+
+| Command | Description |
+|---------|-------------|
+| `deposit <item>` | Move item from inventory to bank |
+| `deposit all` | Deposit entire inventory |
+| `withdraw <item>` | Move item from bank to inventory |
+| `browse` / `list` | Show bank contents |
+| `leave` | Exit bank interface |
+
+## Implementation
+
+### Session State
+
+`StateBank` (defined in `internal/net/server.go`) is the session state for the bank interface. Input is routed through `handleBankInput` in `internal/game/cmd_bank.go`.
+
+### Player Storage
+
+Bank items are stored in the `Player.Bank` field (`map[int]*InventorySlot`), saved in character YAML. Bank slots are sequential and reuse freed slots. There is no slot limit.
+
+### Command Dispatch
+
+- `bank` is classified as `ClassActive` in `classifyCommand()`
+- `bank` case in `executeCommand()` calls `doBank(sess)`
+- `doUse()` checks for `"bank"` or `"bank booth"` targets and routes to `doBank()`
+- `doBank()` checks for a `bank_booth` object in the current room
+- `handleBankInput()` dispatches deposit/withdraw/browse/leave commands
+
+### Data Files
+
+| File | Purpose |
+|------|---------|
+| `data/objects/bank_booth.yaml` | Bank booth object definition |
+| `data/help/bank.yaml` | Help topic for the bank system |
+
+Default bank booth locations: Town Square (room 1), Forge (room 12).