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>

web/dist/style.css

@@ -70,14 +70,14 @@ body,
 }
 
 .login-box .motd {
-  color: var(--text-dim);
-  font-size: 12px;
+  color: var(--accent);
+  font-size: 11px;
   margin-bottom: 20px;
   text-align: left;
-  white-space: pre-wrap;
+  white-space: pre;
   font-family: inherit;
-  border-left: 2px solid var(--border);
-  padding-left: 12px;
+  line-height: 1.2;
+  overflow-x: auto;
 }
 
 .login-box form {