Move the test-only helpers out of the shipped db package (closes #248)

The server binary carried exported names that only tests call, including
raw SQL access and a way to weaken the password hash.

Delete testing.go, GetDB and SetBcryptCost from the shipped code, so
passwords always hash at bcrypt.DefaultCost. Move GetDB, GetOrCreateChannel,
JoinChannel and HasChannelInvite into export_test.go. Delete
GetClientHostInfo, whose remaining check GetLatestClientForSession covers.

Tests in other packages now build the database with db.New and run raw SQL
through dbtest.Exec.

Model: opus-5-5

internal/handlers/api_test.go

@@ -23,7 +23,6 @@ import (
 
 	"go.uber.org/fx"
 	"go.uber.org/fx/fxtest"
-	"golang.org/x/crypto/bcrypt"
 	"modernc.org/sqlite"
 	"sneak.berlin/go/neoirc/internal/broker"
 	api "sneak.berlin/go/neoirc/internal/cli/api"
@@ -863,7 +862,10 @@ func TestRequestBodyLimit(t *testing.T) {
 			tserver := newTestServer(t)
 			token := tserver.createSession(nick)
 
-			tserver.setPassword(nick)
+			tserver.sendCommand(token, map[string]any{
+				commandKey: irc.CmdPass,
+				bodyKey:    []string{testPassword},
+			})
 
 			bytesToLimit := maxMessageSize - len(endpoint.value)
 
@@ -1765,7 +1767,9 @@ func checkQuitRace(
 		firstToken := tserver.createSession(nick)
 		observerToken := tserver.createSession("raceobserver")
 
-		tserver.setPassword(nick)
+		tserver.sendCommand(firstToken, map[string]any{
+			commandKey: irc.CmdPass, bodyKey: []string{testPassword},
+		})
 
 		tokens := []string{firstToken, tserver.login(nick)}
 
@@ -1815,7 +1819,9 @@ func TestLogoutOfOneClientKeepsSession(t *testing.T) {
 	firstToken := tserver.createSession(nick)
 	observerToken := tserver.createSession("logoutobserver")
 
-	tserver.setPassword(nick)
+	tserver.sendCommand(firstToken, map[string]any{
+		commandKey: irc.CmdPass, bodyKey: []string{testPassword},
+	})
 
 	secondToken := tserver.login(nick)
 
@@ -2124,24 +2130,6 @@ func (tserver *testServer) longPoll(
 	return result.Messages, nil
 }
 
-// setPassword gives the session nick the password testPassword
-// without sending PASS. It hashes at bcrypt.MinCost, and a login
-// compares at the cost stored in the hash, so both are fast.
-func (tserver *testServer) setPassword(nick string) {
-	tserver.t.Helper()
-
-	hash, err := bcrypt.GenerateFromPassword(
-		[]byte(testPassword), bcrypt.MinCost,
-	)
-	if err != nil {
-		tserver.t.Fatalf("hash password: %v", err)
-	}
-
-	dbtest.Exec(tserver.t, tserver.dbURL,
-		"UPDATE sessions SET password_hash = '"+string(hash)+
-			"' WHERE nick = '"+nick+"'")
-}
-
 // login logs in to the session nick with testPassword and
 // returns the new client's token.
 func (tserver *testServer) login(nick string) string {
@@ -3749,8 +3737,13 @@ func TestLoginValid(t *testing.T) {
 
 	tserver := newTestServer(t)
 
-	tserver.createSession("loginuser")
-	tserver.setPassword("loginuser")
+	// Create session and set password via PASS command.
+	token := tserver.createSession("loginuser")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: irc.CmdPass,
+		bodyKey:    []string{testPassword},
+	})
 
 	// Login with nick + password.
 	loginBody, err := json.Marshal(map[string]string{
@@ -3814,8 +3807,13 @@ func TestLoginWrongPassword(t *testing.T) {
 
 	tserver := newTestServer(t)
 
-	tserver.createSession("wrongpwuser")
-	tserver.setPassword("wrongpwuser")
+	// Create session and set password via PASS command.
+	token := tserver.createSession("wrongpwuser")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: irc.CmdPass,
+		bodyKey:    []string{"correctpass1"},
+	})
 
 	postJSONExpectStatus(
 		t, tserver, "/api/v1/login",
@@ -4286,8 +4284,13 @@ func TestLoginRateLimitAllowsNormalUse(t *testing.T) {
 
 	tserver := newTestServer(t)
 
-	tserver.createSession("normaluser")
-	tserver.setPassword("normaluser")
+	// Create session and set password via PASS command.
+	token := tserver.createSession("normaluser")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: irc.CmdPass,
+		bodyKey:    []string{testPassword},
+	})
 
 	// A single login should succeed without rate limiting.
 	loginBody, err := json.Marshal(map[string]string{