feat(api): My Wave sessions with a Go fallback and wave metrics (M4)

- /wave/options, POST /wave/sessions (activity, mood, seed),
  /next with reactions, PATCH to switch the context on the fly, DELETE
- the recommender is called with an 800 ms budget; on failure the api
  serves a fallback wave of likes, favourite artists and random
  available tracks with the same dislike / recent / served filters
- every served track is an impression with its source and model; wave
  events (context_type wave) set its outcome, reactions win
- library status shows the analysis queue and 7-day wave metrics:
  listen-through, early skip and like rate

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

services/api/internal/server/router.go

@@ -15,6 +15,7 @@ import (
 	"pipu/api/internal/playback"
 	"pipu/api/internal/search"
 	"pipu/api/internal/system"
+	"pipu/api/internal/wave"
 )
 
 // Deps — модули, реализующие части контракта API.
@@ -27,6 +28,8 @@ type Deps struct {
 	Search  *search.Handler
 	// Playback — стрим, события, история, реакции, состояние плеера.
 	Playback *playback.Handler
+	// Wave — «Моя волна».
+	Wave *wave.Handler
 	// AuthService проверяет access-токены в middleware. nil — только для тестов служебных эндпоинтов.
 	AuthService *auth.Service
 }
@@ -40,6 +43,7 @@ type (
 	libraryHandler  = library.Handler
 	searchHandler   = search.Handler
 	playbackHandler = playback.Handler
+	waveHandler     = wave.Handler
 )
 
 type handlers struct {
@@ -48,6 +52,7 @@ type handlers struct {
 	*libraryHandler
 	*searchHandler
 	*playbackHandler
+	*waveHandler
 }
 
 var _ gen.StrictServerInterface = handlers{}
@@ -67,7 +72,7 @@ func NewRouter(d Deps) http.Handler {
 	r.NotFound(httpx.NotFound)
 	r.MethodNotAllowed(httpx.MethodNotAllowed)
 
-	strict := gen.NewStrictHandlerWithOptions(handlers{systemHandler: d.System, authHandler: d.Auth, libraryHandler: d.Library, searchHandler: d.Search, playbackHandler: d.Playback},
+	strict := gen.NewStrictHandlerWithOptions(handlers{systemHandler: d.System, authHandler: d.Auth, libraryHandler: d.Library, searchHandler: d.Search, playbackHandler: d.Playback, waveHandler: d.Wave},
 		[]gen.StrictMiddlewareFunc{httpx.StrictRequest}, gen.StrictHTTPServerOptions{
 			RequestErrorHandlerFunc:  httpx.RequestError,
 			ResponseErrorHandlerFunc: httpx.ResponseError(log),