Merge branch 'main' into golangci-v2.12.2

Absorbs the cache size management and LRU eviction work (#55). All four
textual conflicts resolved in favor of main's implementation, with this
branch's mechanical lint conformance re-applied on top:

- internal/config/config.go: took main's cache_max_bytes wiring
  (CacheMaxBytes, cacheMaxBytesExplicit) verbatim and expressed the key
  through this branch's constant convention as keyCacheMaxBytes.
- internal/imgcache/cache.go: took main's disabled-cache guards, LRU
  touch on lookup, and variant_content size accounting verbatim;
  re-applied this branch's signature wrapping for lll.
- internal/imgcache/storage.go: took main's new writeIfAbsent helper and
  its temp-file cleanup defer verbatim. The auto-merge had silently
  dropped that defer in favor of this branch's inline cleanup form;
  restored so the cleanup semantics that arrived from main are intact.
- TODO.md: kept both sides' Completed Steps entries.

.golangci.yml resolves to this branch's canonical version
(sha256 021cc83f4e6fc7c31b95b34b846723dfcf20b66b7baeea1dc40406e643346bcb).

make build and make test are green; #55's code is not yet conformant
with the canonical lint config, which the following commits address.

internal/handlers/handlers.go

@@ -54,6 +54,13 @@ func New(lc fx.Lifecycle, params Params) (*Handlers, error) {
 		OnStart: func(_ context.Context) error {
 			return s.initImageService()
 		},
+		OnStop: func(_ context.Context) error {
+			if s.imgCache != nil {
+				s.imgCache.StopEviction()
+			}
+
+			return nil
+		},
 	})
 
 	return s, nil
@@ -61,11 +68,15 @@ func New(lc fx.Lifecycle, params Params) (*Handlers, error) {
 
 // initImageService initializes the image cache and service.
 func (s *Handlers) initImageService() error {
-	// Create the cache
+	// Create the cache. cache_max_bytes: 0 disables the disk cache
+	// entirely; any other value is the eviction limit in bytes.
 	cache, err := imgcache.NewCache(s.db.DB(), imgcache.CacheConfig{
-		StateDir:    s.config.StateDir,
-		CacheTTL:    imgcache.DefaultCacheTTL,
-		NegativeTTL: imgcache.DefaultNegativeTTL,
+		StateDir:         s.config.StateDir,
+		CacheTTL:         imgcache.DefaultCacheTTL,
+		NegativeTTL:      imgcache.DefaultNegativeTTL,
+		MaxBytes:         s.config.CacheMaxBytes,
+		DisableDiskCache: s.config.CacheMaxBytes == 0,
+		Logger:           s.log,
 	})
 	if err != nil {
 		return err
@@ -73,6 +84,10 @@ func (s *Handlers) initImageService() error {
 
 	s.imgCache = cache
 
+	// Background eviction: startup reconciliation, then periodic and
+	// write-pressure passes. No-op when the disk cache is disabled.
+	cache.StartEviction(imgcache.DefaultEvictionInterval)
+
 	// Create the fetcher config
 	fetcherCfg := httpfetcher.DefaultConfig()
 	fetcherCfg.AllowHTTP = s.config.AllowHTTP