fix: IRC SPA cleanup — /motd, /query, Firefox / key, default MOTD (#58)

## Summary

Fixes IRC client SPA issues reported in [issue #57](#57).

## Changes

### Server-side
- **Default MOTD**: Added figlet-style ASCII art MOTD for "neoirc" as the default when no MOTD is configured via environment/config
- **MOTD command handler**: Added `MOTD` case to `dispatchCommand` so clients can re-request the MOTD at any time (proper IRC behavior)

### SPA (web client)
- **`/motd` command**: Sends MOTD request to server, displays 375/372/376 numerics in server window
- **`/query nick [message]`**: Opens a DM tab with the specified user, optionally sends a message
- **`/clear`**: Clears messages in the current tab
- **Firefox `/` key fix**: Added global `keydown` listener that captures `/` when input is not focused, preventing Firefox quick search and redirecting focus to the input element. Also auto-focuses input on SPA init.
- **MOTD on resumed sessions**: When restoring from a saved token, the MOTD is re-requested so it always appears in the server window
- **Updated `/help`**: Shows all new commands with descriptions
- **Login screen MOTD styling**: Improved for ASCII art display (monospace, proper line height)

## Testing
- `docker build .` passes (includes `make check` with tests, lint, fmt-check)
- All existing tests pass with no modifications

closes #57

<!-- session: agent:sdlc-manager:subagent:7c880fec-f818-49ff-a548-2d3c26758bb6 -->

Co-authored-by: user <user@Mac.lan guest wan>
Reviewed-on: #58
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/config/config.go

@@ -13,6 +13,14 @@ import (
 	_ "github.com/joho/godotenv/autoload" // loads .env file
 )
 
+const defaultMOTD = ` _ __   ___  ___  (_)_ __ ___
+| '_ \ / _ \/ _ \ | | '__/ __|
+| | | |  __/ (_) || | | | (__
+|_| |_|\___|\___/ |_|_|  \___|
+
+Welcome to NeoIRC — IRC semantics over HTTP.
+Type /help for available commands.`
+
 // Params defines the dependencies for creating a Config.
 type Params struct {
 	fx.In
@@ -62,7 +70,7 @@ func New(
 	viper.SetDefault("METRICS_PASSWORD", "")
 	viper.SetDefault("MAX_HISTORY", "10000")
 	viper.SetDefault("MAX_MESSAGE_SIZE", "4096")
-	viper.SetDefault("MOTD", "")
+	viper.SetDefault("MOTD", defaultMOTD)
 	viper.SetDefault("SERVER_NAME", "")
 	viper.SetDefault("FEDERATION_KEY", "")
 	viper.SetDefault("SESSION_IDLE_TIMEOUT", "24h")