Restructure backend into services and fix security, crash and sync issues

Security
- Serve character images through os.Root so names like ../ can't escape
  the characters folder
- Sync start and /sync/reset are POST only (legacy and /api/v1)
- /api/v1/token/cleanup requires a token, password compared in constant
  time, tokens no longer logged
- Echo's rate limiter replaces the custom one; TRUSTED_PROXIES enables
  X-Forwarded-For for reverse proxies

Crashes and races
- Sync state lives in SyncService with atomics and a mutex instead of
  unsynchronised globals (fixes concurrent map writes during full sync)
- Only one sync can run; /api/v1 sync and music routes are locked during
  sync like the legacy ones
- No log.Fatal outside startup: errors become 4xx/5xx responses
- Search uses an in-order character match instead of unescaped regexes
- Empty queue / no songs return 404 instead of panicking or looping

Behaviour
- Sync result is computed once and stays the same between polls
- Swagger and /openapi serve the embedded spec
- Shutdown stops HTTP before closing the database
- Expired tokens are deleted with a context that outlives the request
- Files are served with Range support and correct content types; audio
  has no write deadline

Performance
- Migration 000006 adds soundtrack.fingerprint (names, sizes, mtimes) so
  unchanged folders are skipped without reading any files
- Songs are reconciled per soundtrack with one query plus needed writes;
  renames keep play counts
- Moved MUSIC_PATH updates soundtrack and song paths
- .id cleanup only runs for changed soundtracks or a full sync
- Classic random uses one SQL query; Gitea release lookups are cached
  with a timeout

Structure
- internal/config reads all environment variables once
- sqlc emits a Querier interface; backend globals become services
  injected into handlers
- One route registration shared by legacy and /api/v1
- Removed dead code (dbHelper.go, unused middleware, duplicate Gitea
  functions, embedded Swagger UI copy) and lib/pq
- templ and swag pinned as go tools

go.mod

@@ -9,8 +9,7 @@ require (
 	github.com/golang-migrate/migrate/v4 v4.19.1
 	github.com/jackc/pgx/v5 v5.9.2
 	github.com/labstack/echo/v5 v5.1.1
-	github.com/lib/pq v1.12.3
-	github.com/panjf2000/ants/v2 v2.12.0
+	github.com/lib/pq v1.12.3 // indirect
 	github.com/spf13/afero v1.15.0
 	github.com/stretchr/testify v1.11.1
 	github.com/swaggo/echo-swagger/v2 v2.0.1
@@ -19,25 +18,34 @@ require (
 	go.uber.org/zap v1.28.0
 )
 
-require github.com/google/uuid v1.6.0
+require (
+	github.com/google/uuid v1.6.0
+	golang.org/x/sync v0.20.0
+)
 
 require (
 	dario.cat/mergo v1.0.2 // indirect
 	github.com/Azure/go-ansiterm v0.0.0-20250102033503-faa5f7b0171c // indirect
 	github.com/KyleBanks/depth v1.2.1 // indirect
 	github.com/Microsoft/go-winio v0.6.2 // indirect
+	github.com/a-h/parse v0.0.0-20250122154542-74294addb73e // indirect
+	github.com/andybalholm/brotli v1.1.0 // indirect
 	github.com/cenkalti/backoff/v4 v4.3.0 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/cli/browser v1.3.0 // indirect
 	github.com/containerd/errdefs v1.0.0 // indirect
 	github.com/containerd/errdefs/pkg v0.3.0 // indirect
 	github.com/containerd/log v0.1.0 // indirect
 	github.com/containerd/platforms v0.2.1 // indirect
 	github.com/cpuguy83/dockercfg v0.3.2 // indirect
+	github.com/cpuguy83/go-md2man/v2 v2.0.5 // indirect
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
 	github.com/distribution/reference v0.6.0 // indirect
 	github.com/docker/go-units v0.5.0 // indirect
 	github.com/ebitengine/purego v0.10.0 // indirect
+	github.com/fatih/color v1.16.0 // indirect
 	github.com/felixge/httpsnoop v1.0.4 // indirect
+	github.com/fsnotify/fsnotify v1.7.0 // indirect
 	github.com/go-errors/errors v1.5.1 // indirect
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
@@ -52,12 +60,15 @@ require (
 	github.com/go-openapi/swag/stringutils v0.26.0 // indirect
 	github.com/go-openapi/swag/typeutils v0.26.0 // indirect
 	github.com/go-openapi/swag/yamlutils v0.26.0 // indirect
+	github.com/jackc/pgerrcode v0.0.0-20220416144525-469b46aa5efa // indirect
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
 	github.com/jackc/puddle/v2 v2.2.2 // indirect
 	github.com/klauspost/compress v1.18.5 // indirect
 	github.com/lufia/plan9stats v0.0.0-20211012122336-39d0f177ccd0 // indirect
 	github.com/magiconair/properties v1.8.10 // indirect
+	github.com/mattn/go-colorable v0.1.13 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/moby/docker-image-spec v1.3.1 // indirect
 	github.com/moby/go-archive v0.2.0 // indirect
 	github.com/moby/moby/api v1.54.1 // indirect
@@ -67,10 +78,12 @@ require (
 	github.com/moby/sys/user v0.4.0 // indirect
 	github.com/moby/sys/userns v0.1.0 // indirect
 	github.com/moby/term v0.5.2 // indirect
+	github.com/natefinch/atomic v1.0.1 // indirect
 	github.com/opencontainers/go-digest v1.0.0 // indirect
 	github.com/opencontainers/image-spec v1.1.1 // indirect
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
 	github.com/power-devops/perfstat v0.0.0-20240221224432-82ca36839d55 // indirect
+	github.com/russross/blackfriday/v2 v2.1.0 // indirect
 	github.com/shirou/gopsutil/v4 v4.26.3 // indirect
 	github.com/sirupsen/logrus v1.9.4 // indirect
 	github.com/sv-tools/openapi v0.4.0 // indirect
@@ -78,6 +91,8 @@ require (
 	github.com/swaggo/swag/v2 v2.0.0-rc5 // indirect
 	github.com/tklauser/go-sysconf v0.3.16 // indirect
 	github.com/tklauser/numcpus v0.11.0 // indirect
+	github.com/urfave/cli/v2 v2.27.5 // indirect
+	github.com/xrash/smetrics v0.0.0-20240521201337-686a1a2994c1 // indirect
 	github.com/yusufpapurcu/wmi v1.2.4 // indirect
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
 	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.61.0 // indirect
@@ -87,9 +102,9 @@ require (
 	go.uber.org/multierr v1.10.0 // indirect
 	go.yaml.in/yaml/v2 v2.4.4 // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
-	golang.org/x/crypto v0.48.0 // indirect
+	golang.org/x/crypto v0.51.0 // indirect
 	golang.org/x/mod v0.36.0 // indirect
-	golang.org/x/sync v0.20.0 // indirect
+	golang.org/x/net v0.54.0 // indirect
 	golang.org/x/sys v0.44.0 // indirect
 	golang.org/x/text v0.37.0 // indirect
 	golang.org/x/time v0.15.0 // indirect
@@ -97,3 +112,8 @@ require (
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 	sigs.k8s.io/yaml v1.6.0 // indirect
 )
+
+tool (
+	github.com/a-h/templ/cmd/templ
+	github.com/swaggo/swag/cmd/swag
+)