Bring README.md in line with the modes and the schema (closes #119)

The MODE section described a query-only command. It now covers channel
and user mode queries and changes on the HTTP API and the IRC listener,
the letters each accepts, what is broadcast, and the error numerics.
The schema section now lists every table and column in
001_initial.sql.

Every other statement this change touches was checked against the code:
polled numerics carry their name in command and their number in code;
command errors are numerics with HTTP 200; the broker is keyed by
session; WAL is never on; a hostname falls back to the IP and is
public; and the IRC listener handles modes, NOTICE, INVITE, +s and +H
more narrowly, with gaps in its bridge to the HTTP API.

Model: opus-5-5

internal/ircserver/server_test.go

@@ -2,7 +2,6 @@ package ircserver_test
 
 import (
 	"bufio"
-	"crypto/rand"
 	"database/sql"
 	"fmt"
 	"log/slog"
@@ -70,11 +69,9 @@ func newTestEnvWithConfig(
 ) *testEnv {
 	t.Helper()
 
-	// A random name, so that no other test environment, not
-	// even an earlier run of the same test, can share it.
 	dsn := fmt.Sprintf(
 		"file:%s?mode=memory&cache=shared&_journal_mode=WAL",
-		rand.Text(),
+		t.Name(),
 	)
 
 	conn, err := sql.Open("sqlite", dsn)
@@ -82,13 +79,6 @@ func newTestEnvWithConfig(
 		t.Fatalf("open db: %v", err)
 	}
 
-	t.Cleanup(func() {
-		err := conn.Close()
-		if err != nil {
-			t.Logf("close db: %v", err)
-		}
-	})
-
 	conn.SetMaxOpenConns(1)
 
 	_, err = conn.ExecContext(
@@ -133,9 +123,14 @@ func newTestEnvWithConfig(
 		t.Fatalf("start irc server: %v", err)
 	}
 
-	// Cleanups run last registered first, so the server stops
-	// before its database is closed.
-	t.Cleanup(srv.Stop)
+	t.Cleanup(func() {
+		srv.Stop()
+
+		err := conn.Close()
+		if err != nil {
+			t.Logf("close db: %v", err)
+		}
+	})
 
 	return &testEnv{
 		database: database,
@@ -347,20 +342,6 @@ func TestRegistration(t *testing.T) {
 	assertContains(t, lines, " 001 ", "RPL_WELCOME")
 }
 
-// TestEachTestEnvHasItsOwnDatabase checks that a test
-// environment starts on an empty database while another one
-// is still open.
-func TestEachTestEnvHasItsOwnDatabase(t *testing.T) {
-	t.Parallel()
-
-	first := newTestEnv(t)
-	first.dial(t).register("samenick")
-
-	second := newTestEnv(t)
-	lines := second.dial(t).register("samenick")
-	assertContains(t, lines, " 001 ", "RPL_WELCOME")
-}
-
 func TestWelcomeContainsNick(t *testing.T) {
 	t.Parallel()