feat(stats): reading statistics — session capture wired + /stats page + widget + per-book card

The design parked in the handoff (multi-tier stats off reading_history;
bookorbit-style in data, not looks) is in. The real prerequisite work
was data: reading_history existed but NOTHING wrote to it — the whole
stats feature was sitting on an empty table.

- CAPTURE (no client changes, no repo-boundary crossings): every
  successful progress write through SaveProgress (KOReader + app + web
  + Kobo + offline queue — the one chokepoint) now records one
  reading_history session row: span = the interval since the PREVIOUS
  write instant, pages = positive page delta when both sides know the
  page index, marker rows for first contact. Spans over 2h are kept as
  zero-second markers (overnight suspend→resume, offline flushes must
  not inflate totals) — the honest 'sync cadence, not a stopwatch'
  caveat stays. device_id only when a REAL device row matches (the
  web/app progress path historically stuffs the USER id into DeviceID
  — probe instead of trusting it; FK violation would silently drop
  every capture). Source preserved in device_metadata.

- API: /api/stats/summary?range=7|30|90|year (totals, zero-filled
  daily arrays, streaks, most-active day/weekday, top books, library
  breakdown — one call), /api/stats/this-week (widget: rolling 7d vs
  previous + streak), /api/stats/books/:id (lifetime + recent
  sessions). All bucketed in the user's timezone; finished ≡ any push
  ≥0.995; visible-library lens enforced at source. Legacy
  /api/analytics/* kept untouched. Range windows anchor end-of-day to
  the START of today (blasting the clock time into tomorrow resolved
  'today' a calendar day late — found by the streak test).

- /stats page (sidebar Stats between Progress and Devices, previously
  /analytics was an orphan): range selector, five stat cards, two
  Chart.js v4 charts (daily minutes bar, pages/day line — chunked via
  dynamic import so main.js stays untouched), per-library breakdown,
  most-read list, empty-state explainer. /analytics now 301s to /stats.
  The orphaned analytics.templ + analytics.ts removed (their containers
  and the page JSON never matched; the page was astub).

- Dashboard 'This Week' widget (server-rendered, suppressed on service
  failure) and the book detail 'Your Reading Stats' card (lifetime
  totals of the viewer's own sessions) complete the tiers: per-user
  default, per-library breakdown inline, per-book on the page,
  per-system/admin aggregate parked as before.

Tests: statistics_test.go (capture semantics at the chokepoint,
tz/day buckets, zero-fill, streak math, finished detection, range
validation, auth gate, widget, per-book lifetime). Full suite PASS.

internal/handlers/media_detail.go

@@ -16,6 +16,11 @@ type MediaDetail struct {
 	Collections     []database.Collections    `json:"collections"`
 	ReadingProgress *database.ReadingProgress `json:"reading_progress,omitempty"`
 
+	// The viewer's own reading-history card for this book (nil when the
+	// user has no sessions here); rendered as the "Your Reading Stats"
+	// section of the book page.
+	BookStats *BookStatsData `json:"book_stats,omitempty"`
+
 	// Conflict data (if exists)
 	ActiveConflict *ConflictDetailResponse `json:"active_conflict,omitempty"`
 
@@ -27,3 +32,14 @@ type MediaDetail struct {
 	// page's "recently deleted" list with restore/permanent-delete actions.
 	DeletedAnnotations []DeletedAnnotationResponse `json:"deleted_annotations"`
 }
+
+// BookStatsData is the per-book reading-stats card payload.
+type BookStatsData struct {
+	TotalMinutes int
+	TotalPages   int
+	SessionCount int
+	MaxProgress  float64 // 0..1
+	Finished     bool
+	LastSession  string
+	FirstSession string
+}

internal/handlers/stats.go

@@ -0,0 +1,88 @@
+package handlers
+
+import (
+	"bookhoard/internal/database"
+	"bookhoard/internal/services"
+	"net/http"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5/pgtype"
+	"github.com/labstack/echo/v5"
+)
+
+// StatsHandler serves the reading-statistics API (/api/stats/*) backed
+// by the StatisticsService. The server owns every conversion: clients
+// receive user-timezone-rendered strings plus raw minute/page counts.
+type StatsHandler struct {
+	statsService *services.StatisticsService
+}
+
+func NewStatsHandler(statsService *services.StatisticsService) *StatsHandler {
+	return &StatsHandler{statsService: statsService}
+}
+
+func mustUser(c *echo.Context) (database.Users, bool) {
+	user, ok := c.Get("user").(database.Users)
+	return user, ok
+}
+
+// Summary handles GET /api/stats/summary?range=7|30|90|year — the /stats
+// page's complete payload: totals, daily arrays, streaks, most-active
+// day, top books, per-library breakdown.
+func (h *StatsHandler) Summary(c *echo.Context) error {
+	user, ok := mustUser(c)
+	if !ok {
+		return echo.NewHTTPError(http.StatusUnauthorized, "invalid user")
+	}
+	summary, err := h.statsService.UserSummary(c.Request().Context(),
+		pgtype.UUID{Bytes: user.ID.Bytes, Valid: true},
+		user.Timezone.String,
+		c.QueryParam("range"),
+	)
+	if err != nil {
+		if err.Error()[:7] == "invalid" {
+			return echo.NewHTTPError(http.StatusBadRequest, err.Error())
+		}
+		return echo.NewHTTPError(http.StatusInternalServerError, err.Error())
+	}
+	return c.JSON(http.StatusOK, summary)
+}
+
+// ThisWeek handles GET /api/stats/this-week — the dashboard widget's
+// data: rolling 7-day totals vs the previous seven days, plus streak.
+func (h *StatsHandler) ThisWeek(c *echo.Context) error {
+	user, ok := mustUser(c)
+	if !ok {
+		return echo.NewHTTPError(http.StatusUnauthorized, "invalid user")
+	}
+	week, err := h.statsService.ThisWeek(c.Request().Context(),
+		pgtype.UUID{Bytes: user.ID.Bytes, Valid: true},
+		user.Timezone.String,
+	)
+	if err != nil {
+		return echo.NewHTTPError(http.StatusInternalServerError, err.Error())
+	}
+	return c.JSON(http.StatusOK, week)
+}
+
+// BookStats handles GET /api/stats/books/:id — the per-book card on the
+// book detail page (lifetime totals + recent sessions).
+func (h *StatsHandler) BookStats(c *echo.Context) error {
+	user, ok := mustUser(c)
+	if !ok {
+		return echo.NewHTTPError(http.StatusUnauthorized, "invalid user")
+	}
+	mediaItemID, err := uuid.Parse(c.Param("id"))
+	if err != nil {
+		return echo.NewHTTPError(http.StatusBadRequest, "invalid media item id")
+	}
+	stats, err := h.statsService.BookStats(c.Request().Context(),
+		pgtype.UUID{Bytes: user.ID.Bytes, Valid: true},
+		mediaItemID,
+		user.Timezone.String,
+	)
+	if err != nil {
+		return echo.NewHTTPError(http.StatusInternalServerError, err.Error())
+	}
+	return c.JSON(http.StatusOK, stats)
+}