Add stats, profiles, avatars and palaute

Step 6. The surfaces around the review loop.

- Nine leaderboards, ordered and limited in SQL, each with a deterministic
  tie-break so a tied board doesn't reshuffle between reloads. Min 3 reviews
  to qualify, for reviewer boards too
- Profiles show counts and history-wide averages and the member's songs,
  never a list of their reviews — per-song opinion stays gated
- Avatars: 5MB in, 256px JPEG out, ffmpeg's re-encode being the validation.
  No upload still means initials, and avatars are public
- Changing your own password requires the current one and drops your other
  sessions
- Palaute: free text plus the page you were on, carried in a footer link, and
  the user agent from the header. Reporters see their own; the admin resolves
  them with a timestamp rather than a status enum
- Admin gained the song list with delete, the reports page, and an open-report
  count on the dashboard

Two theme fixes the screenshots caught: leaderboard ranks need a CSS counter
because display:grid suppresses list markers, and count-based boards were
printing 3.0 where they mean 3.

templates/stats.html

@@ -0,0 +1,56 @@
+{{define "songboard"}}
+<section class="board">
+  <h2>{{.Title}}</h2>
+  {{if .Items}}
+    <ol class="board-list">
+      {{range .Items}}
+        <li>
+          <a href="/songs/{{.ID}}">{{.Title}}</a>
+          <span class="muted small">{{.Artist}}</span>
+          <span class="value">{{if $.Count}}{{.ReviewCount}}{{else}}{{value .Value}}{{end}}</span>
+          {{if not $.Count}}<span class="muted small">{{.ReviewCount}} arv.</span>{{end}}
+        </li>
+      {{end}}
+    </ol>
+  {{else}}
+    <p class="muted small">Ei vielä tarpeeksi arvosteluja.</p>
+  {{end}}
+</section>
+{{end}}
+
+{{define "userboard"}}
+<section class="board">
+  <h2>{{.Title}}</h2>
+  {{if .Items}}
+    <ol class="board-list">
+      {{range .Items}}
+        <li>
+          <a href="/profile/{{.ID}}">{{.Name}}</a>
+          <span class="value">{{if $.Count}}{{.Count}}{{else}}{{value .Value}}{{end}}</span>
+          {{if not $.Count}}<span class="muted small">{{.Count}} kpl</span>{{end}}
+        </li>
+      {{end}}
+    </ol>
+  {{else}}
+    <p class="muted small">Ei vielä tarpeeksi arvosteluja.</p>
+  {{end}}
+</section>
+{{end}}
+
+{{define "content"}}
+<h1>Tilastot</h1>
+<p class="muted">Kappale pääsee listoille kun sillä on vähintään {{.Data.MinReviews}} arvostelua.
+  Tilastot näkyvät kaikille — täällä pisteitä ei piiloteta.</p>
+
+<div class="boards">
+  {{template "songboard" dict "Title" "Parhaat" "Items" .Data.TopSongs}}
+  {{template "songboard" dict "Title" "Heikoimmat" "Items" .Data.BottomSongs}}
+  {{template "songboard" dict "Title" "Riitaisimmat" "Items" .Data.MostDivisive}}
+  {{template "songboard" dict "Title" "Yksimielisimmät" "Items" .Data.MostUnified}}
+  {{template "songboard" dict "Title" "Eniten arvosteltu" "Items" .Data.MostReviewed "Count" true}}
+  {{template "userboard" dict "Title" "Ankarin arvostelija" "Items" .Data.Harshest}}
+  {{template "userboard" dict "Title" "Anteliain" "Items" .Data.MostGenerous}}
+  {{template "userboard" dict "Title" "Ahkerin arvostelija" "Items" .Data.MostActive "Count" true}}
+  {{template "userboard" dict "Title" "Ahkerin lähettäjä" "Items" .Data.MostProlific "Count" true}}
+</div>
+{{end}}