refactor: move CLI code from cmd/ to internal/cli/

Move all substantive CLI code (app logic, UI, API client,
hashcash, types) from cmd/neoirc-cli/ to internal/cli/.
The cmd/neoirc-cli/main.go now contains only minimal
bootstrapping that calls cli.Run().

This follows the project convention that cmd/ should only
contain minimal main() bootstrapping code.

README.md

@@ -2311,18 +2311,15 @@ neoirc/
 ├── cmd/
 │   ├── neoircd/            # Server binary entry point
 │   │   └── main.go
-│   └── neoirc-cli/         # TUI client entry point
-│       └── main.go         # Minimal bootstrapping (calls internal/cli)
+│   └── neoirc-cli/         # TUI client
+│       ├── main.go         # Command handling, poll loop
+│       ├── ui.go           # tview-based terminal UI
+│       └── api/
+│           ├── client.go   # HTTP API client library
+│           └── types.go    # Request/response types
 ├── internal/
 │   ├── broker/             # In-memory pub/sub for long-poll notifications
 │   │   └── broker.go
-│   ├── cli/                # TUI client implementation
-│   │   ├── app.go          # App struct, command handling, poll loop
-│   │   ├── ui.go           # tview-based terminal UI
-│   │   └── api/
-│   │       ├── client.go   # HTTP API client library
-│   │       ├── types.go    # Request/response types
-│   │       └── hashcash.go # Hashcash proof-of-work minting
 │   ├── config/             # Viper-based configuration
 │   │   └── config.go
 │   ├── db/                 # Database access and migrations

cmd/neoirc-cli/main.go

@@ -1,8 +1,17 @@
 // Package main is the entry point for the neoirc-cli client.
 package main
 
-import "git.eeqj.de/sneak/neoirc/internal/cli"
+import (
+	"fmt"
+	"os"
+
+	"git.eeqj.de/sneak/neoirc/internal/cli"
+)
 
 func main() {
-	cli.Run()
+	err := cli.Run()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+		os.Exit(1)
+	}
 }

internal/cli/app.go

@@ -1,9 +1,8 @@
-// Package cli implements the neoirc-cli terminal client.
+// Package cli implements the neoirc-cli client logic.
 package cli
 
 import (
 	"fmt"
-	"os"
 	"strings"
 	"sync"
 	"time"
@@ -32,8 +31,8 @@ type App struct {
 	stopPoll  chan struct{}
 }
 
-// Run creates and runs the CLI application.
-func Run() {
+// Run starts the neoirc-cli application.
+func Run() error {
 	app := &App{ //nolint:exhaustruct
 		ui:   NewUI(),
 		nick: "guest",
@@ -51,11 +50,7 @@ func Run() {
 			"or [yellow]/help[white] for commands",
 	)
 
-	err := app.ui.Run()
-	if err != nil {
-		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
-		os.Exit(1)
-	}
+	return app.ui.Run()
 }
 
 func (a *App) handleInput(text string) {