Build the image pipeline in pixad's fx graph (closes #313)

The new package internal/providers builds the cache, the fetcher, the
processor, the image service, the session manager and the encrypted URL
generator from the config. pixad's fx graph provides them with
providers.Constructors(), and handlers.New receives them built. The
server tests build the same graph, with only the fetcher's dial function
replaced. database.New opens the database, so these parts can read it
while fx builds them; the cache's stop hook still runs before the
database's.

Each setting's default is declared in internal/config, and
internal/providers works out the default cache_max_bytes. The cache's
MaxBytes is the one value for the disk cache limit, and 0 turns the disk
cache off. The fetcher and the processor take explicit values.

Model: opus-5-5

internal/imgcache/negative_cache_internal_test.go

@@ -20,6 +20,7 @@ func TestNegativeCache_StoreAndCheck(t *testing.T) {
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    dir,
 		NegativeTTL: 5 * time.Minute,
+		MaxBytes:    1 << 30,
 	}, prometheus.NewRegistry())
 	if err != nil {
 		t.Fatal(err)
@@ -69,6 +70,7 @@ func TestNegativeCache_Expired(t *testing.T) {
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    dir,
 		NegativeTTL: 1 * time.Millisecond, // very short TTL
+		MaxBytes:    1 << 30,
 	}, prometheus.NewRegistry())
 	if err != nil {
 		t.Fatal(err)
@@ -177,11 +179,11 @@ func TestEvictionLoopRemovesExpiredNegativeCacheRows(t *testing.T) {
 	t.Parallel()
 
 	tests := []struct {
-		name             string
-		disableDiskCache bool
+		name     string
+		maxBytes int64
 	}{
-		{name: "disk cache enabled", disableDiskCache: false},
-		{name: "disk cache disabled", disableDiskCache: true},
+		{name: "disk cache enabled", maxBytes: 1 << 30},
+		{name: "disk cache disabled", maxBytes: 0},
 	}
 
 	for _, tt := range tests {
@@ -189,9 +191,9 @@ func TestEvictionLoopRemovesExpiredNegativeCacheRows(t *testing.T) {
 			t.Parallel()
 
 			cache, err := NewCache(evictionTestDB(t), CacheConfig{
-				StateDir:         t.TempDir(),
-				NegativeTTL:      time.Second,
-				DisableDiskCache: tt.disableDiskCache,
+				StateDir:    t.TempDir(),
+				NegativeTTL: time.Second,
+				MaxBytes:    tt.maxBytes,
 			}, prometheus.NewRegistry())
 			if err != nil {
 				t.Fatalf("failed to create cache: %v", err)
@@ -266,7 +268,8 @@ func negativeCacheRowCount(tb testing.TB, cache *Cache, sourcePath string) int {
 func TestCleanExpiredDeletesInBatches(t *testing.T) {
 	t.Parallel()
 
-	cache, err := NewCache(evictionTestDB(t), CacheConfig{StateDir: t.TempDir()},
+	cache, err := NewCache(evictionTestDB(t),
+		CacheConfig{StateDir: t.TempDir(), MaxBytes: 1 << 30},
 		prometheus.NewRegistry())
 	if err != nil {
 		t.Fatalf("failed to create cache: %v", err)
@@ -321,7 +324,8 @@ func TestCleanExpiredDeletesInBatches(t *testing.T) {
 func TestCleanExpiredRemovesMoreThanOneBatch(t *testing.T) {
 	t.Parallel()
 
-	cache, err := NewCache(evictionTestDB(t), CacheConfig{StateDir: t.TempDir()},
+	cache, err := NewCache(evictionTestDB(t),
+		CacheConfig{StateDir: t.TempDir(), MaxBytes: 1 << 30},
 		prometheus.NewRegistry())
 	if err != nil {
 		t.Fatalf("failed to create cache: %v", err)
@@ -352,7 +356,8 @@ func TestCleanExpiredRemovesMoreThanOneBatch(t *testing.T) {
 func TestCleanExpiredStopsOnceContextEnds(t *testing.T) {
 	t.Parallel()
 
-	cache, err := NewCache(evictionTestDB(t), CacheConfig{StateDir: t.TempDir()},
+	cache, err := NewCache(evictionTestDB(t),
+		CacheConfig{StateDir: t.TempDir(), MaxBytes: 1 << 30},
 		prometheus.NewRegistry())
 	if err != nil {
 		t.Fatalf("failed to create cache: %v", err)