fix: use in-memory SQLite for handler tests to fix CI timeout (#93)

## Summary

Fixes the CI build failure caused by the `internal/handlers` test package exceeding the 30-second per-package timeout on the x86_64 CI runner.

## Root Cause

Each of the 104 handler tests was creating a **file-backed SQLite database** in a temp directory with WAL journaling. On slower CI runners (x86_64 ubuntu-latest), the cumulative filesystem I/O overhead for 104 DB create + migrate + teardown cycles pushed the package well past the 30s timeout.

## Fix

1. **In-memory SQLite** — Switch test databases from `file:<tmpdir>/test.db?_journal_mode=WAL&_busy_timeout=5000` to `file:test_<ptr>?mode=memory&cache=shared`. Each test still gets its own isolated database (unique name per `*testing.T` pointer), but without filesystem I/O.

2. **Consolidated test server constructors** — Merged the duplicate `newTestServer()` and `newTestServerWithOper()` setup code into a shared `newTestServerWith()` helper, removing ~50 lines of duplication.

## Results

| Environment | Before | After |
|---|---|---|
| ARM native (no race) | ~4.5s | ~2.0s |
| ARM native (with race) | ~11.5s | ~8.7s |
| Docker ARM (with race+cover) | **~20.4s** | **~10.0s** |

The Docker ARM time is the closest proxy for CI. With the ~2x overhead of x86_64 emulation on CI, the estimated CI time is ~20s — well within the 30s timeout.

## What This Does NOT Change

- No test assertions modified
- No tests skipped or removed
- No linter config changes
- No Makefile changes
- No CI config changes
- All 104 handler tests still run with full isolation

closes #90

Co-authored-by: clawbot <clawbot@noreply.git.eeqj.de>
Reviewed-on: #93
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/handlers/api_test.go

@@ -12,7 +12,6 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"os"
-	"path/filepath"
 	"strconv"
 	"strings"
 	"sync"
@@ -64,12 +63,20 @@ func newTestServer(
 ) *testServer {
 	t.Helper()
 
-	dbPath := filepath.Join(
-		t.TempDir(), "test.db",
-	)
+	return newTestServerWith(t, 0, "", "")
+}
 
-	dbURL := "file:" + dbPath +
-		"?_journal_mode=WAL&_busy_timeout=5000"
+func newTestServerWith(
+	t *testing.T,
+	hashcashBits int,
+	operName, operPassword string,
+) *testServer {
+	t.Helper()
+
+	dbURL := fmt.Sprintf(
+		"file:test_%p?mode=memory&cache=shared",
+		t,
+	)
 
 	var srv *server.Server
 
@@ -95,7 +102,9 @@ func newTestServer(
 
 				cfg.DBURL = dbURL
 				cfg.Port = 0
-				cfg.HashcashBits = 0
+				cfg.HashcashBits = hashcashBits
+				cfg.OperName = operName
+				cfg.OperPassword = operPassword
 
 				return cfg, nil
 			},
@@ -3055,67 +3064,9 @@ func newTestServerWithOper(
 ) *testServer {
 	t.Helper()
 
-	dbPath := filepath.Join(
-		t.TempDir(), "test.db",
+	return newTestServerWith(
+		t, 0, testOperName, testOperPassword,
 	)
-
-	dbURL := "file:" + dbPath +
-		"?_journal_mode=WAL&_busy_timeout=5000"
-
-	var srv *server.Server
-
-	app := fxtest.New(t,
-		fx.Provide(
-			newTestGlobals,
-			logger.New,
-			func(
-				lifecycle fx.Lifecycle,
-				globs *globals.Globals,
-				log *logger.Logger,
-			) (*config.Config, error) {
-				cfg, err := config.New(
-					lifecycle, config.Params{ //nolint:exhaustruct
-						Globals: globs, Logger: log,
-					},
-				)
-				if err != nil {
-					return nil, fmt.Errorf(
-						"test config: %w", err,
-					)
-				}
-
-				cfg.DBURL = dbURL
-				cfg.Port = 0
-				cfg.HashcashBits = 0
-				cfg.OperName = testOperName
-				cfg.OperPassword = testOperPassword
-
-				return cfg, nil
-			},
-			newTestDB,
-			stats.New,
-			newTestHealthcheck,
-			newTestMiddleware,
-			newTestHandlers,
-			newTestServerFx,
-		),
-		fx.Populate(&srv),
-	)
-
-	app.RequireStart()
-
-	httpSrv := httptest.NewServer(srv)
-
-	t.Cleanup(func() {
-		httpSrv.Close()
-		app.RequireStop()
-	})
-
-	return &testServer{
-		httpServer: httpSrv,
-		t:          t,
-		fxApp:      app,
-	}
 }
 
 func TestOperCommandSuccess(t *testing.T) {