feat: metrics dashboards with SVG charts, CSV export, leaderboard (phase 10)

- aggregations over the immutable bountyAwards ledger: totals, weekly
  buckets ($dateTrunc), per-developer and per-customer groupings
- timeline-derived: approval rate, time logged, assigned→approved lead
  time, imported→published atomization lead time, open board depth
- developer + consultant dashboards (admin = global consultant view),
  date-range filters, CSV export of the ledger
- leaderboard (top 10 by bounty) honoring the new leaderboardOptOut
  profile setting
- hand-rolled SVG line and bar charts (~150 lines, no chart library)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/templates/metrics.html

@@ -0,0 +1,45 @@
+{{define "content"}}
+<div class="spread">
+  <h1>Metrics</h1>
+  <span>
+    <label class="muted" style="display:inline">From <input type="date" id="m-from" style="width:auto"></label>
+    <label class="muted" style="display:inline">To <input type="date" id="m-to" style="width:auto"></label>
+    <button class="btn small" id="m-apply">Apply</button>
+    <a class="btn small" id="m-csv" href="#">Export CSV</a>
+  </span>
+</div>
+<div class="error-box" id="error" role="alert"></div>
+
+<section id="dev-metrics" hidden>
+  <div class="grid mt" id="dev-cards"></div>
+  <div class="card mt"><h2>Earnings over time (weekly)</h2><div id="dev-weekly"></div></div>
+  <div class="card mt"><h2>Per customer</h2><div id="dev-customers"></div></div>
+</section>
+
+<section id="cons-metrics" hidden>
+  <div class="spread mt">
+    <span>
+      <label class="muted" style="display:inline">Customer
+        <select id="m-customer" style="width:auto"><option value="">All</option></select>
+      </label>
+    </span>
+  </div>
+  <div class="grid mt" id="cons-cards"></div>
+  <div class="card mt"><h2>Awarded over time (weekly)</h2><div id="cons-weekly"></div></div>
+  <div class="row mt">
+    <div class="card"><h2>Per developer</h2><div id="cons-devs"></div></div>
+    <div class="card"><h2>Per customer</h2><div id="cons-customers"></div></div>
+  </div>
+</section>
+
+<div class="card mt">
+  <div class="spread">
+    <h2>Leaderboard — top developers</h2>
+    <label class="muted"><input type="checkbox" id="lb-optout"> Hide me from the leaderboard</label>
+  </div>
+  <table class="list" id="leaderboard">
+    <thead><tr><th>#</th><th>Developer</th><th>Tasks</th><th>Bounty</th></tr></thead>
+    <tbody></tbody>
+  </table>
+</div>
+{{end}}