Add paid-traffic tracking: clickid capture and BeMob conversion postback

- track.js stores ?clickid= (or ?cid=) for the session; rides through
  bridge -> start navigation alongside the existing source attribution.
- Join click (the conversion) sends the clickid; server fires a
  fire-and-forget S2S postback to the admin-configured BeMob postback
  URL (cid + txid=join-<clickid>, payout 0) and counts successes per
  source in analytics.
- New admin setting: BeMob postback URL (server-side only, not exposed
  in public config).

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

public/admin.html

@@ -5,5 +5,5 @@
 <div class="table-card"><div style="margin-bottom:12px"><h2 style="margin:0">Traffic &amp; Conversions</h2><p style="color:var(--muted);margin:4px 0 0;font-size:13px">First-touch source per visitor session (referring domain or utm_source). Funnel: bridge page → start page → join click.</p></div><div id="funnelStats" class="funnel"></div><div class="table-wrap"><table class="table"><thead><tr><th>Source</th><th>Bridge views</th><th>Start views</th><th>Training views</th><th>Join clicks</th><th>Start → Join</th></tr></thead><tbody id="trafficRows"></tbody></table></div></div></div>
 <div class="stack"><div class="table-card"><h2 style="margin-top:0">Add Sponsor</h2><form id="addSponsorForm"><div class="form-grid"><div class="field"><label>ID</label><input name="id" class="input" required></div><div class="field"><label>Name</label><input name="name" class="input" required></div><div class="field"><label>Parent ID</label><input name="parentId" class="input"></div><div class="field"><label>Level</label><select name="level" class="select"><option>Scintilla</option><option>Ascensus</option><option>Fabrica</option><option>Culmen</option><option>Apex</option><option>Fastigium</option><option>Vertex</option><option>Corona</option></select></div></div><div class="field"><label>Notes</label><input name="notes" class="input"></div><button class="btn btn-teal" style="width:100%">Add to Queue</button></form></div>
 <div class="table-card"><h2 style="margin-top:0">AI Chat</h2><p style="color:var(--muted);font-size:13px;margin:4px 0 12px">Paste an OpenRouter API key to switch the help chat from canned answers to AI (<span id="aiModel"></span>). Clear it to switch back.</p><div id="aiStatus" class="micro" style="margin-bottom:10px"></div><form id="aiKeyForm"><div class="field"><label>OpenRouter API key</label><input name="key" class="input" type="password" placeholder="sk-or-v1-…" autocomplete="off"></div><button class="btn btn-teal" style="width:100%">Save Key</button><button type="button" id="aiKeyClear" class="btn btn-secondary" style="width:100%;margin-top:8px">Clear Key (use canned answers)</button></form></div>
-<div class="table-card"><h2 style="margin-top:0">Public Page Settings</h2><form id="configForm"><div class="field"><label>Site name</label><input name="siteName" class="input"></div><div class="field"><label>Program name</label><input name="programName" class="input"></div><div class="field"><label>Bridge headline</label><input name="bridgeHeadline" class="input"></div><div class="field"><label>Bridge subheadline</label><textarea name="bridgeSubheadline" class="input" rows="3"></textarea></div><div class="field"><label>Premium entry (POL)</label><input name="premiumEntryPol" class="input" type="number"></div><div class="field"><label>RM dApp referral base URL</label><input name="dappReferralBaseUrl" class="input" placeholder="https://app.thermcircle.com?ref="></div><div class="field"><label>Telegram/support URL (optional)</label><input name="telegramUrl" class="input"></div><div class="field"><label>Support message</label><textarea name="supportLabel" class="input" rows="3"></textarea></div><label style="text-transform:none;letter-spacing:0;margin:10px 0"><input type="checkbox" name="showSponsorName"> Show sponsor name publicly</label><label style="text-transform:none;letter-spacing:0;margin:10px 0"><input type="checkbox" name="showQueueProgress"> Show number waiting in queue</label><button class="btn btn-primary" style="width:100%;margin-top:8px">Save Settings</button></form></div></div></div></section>
+<div class="table-card"><h2 style="margin-top:0">Public Page Settings</h2><form id="configForm"><div class="field"><label>Site name</label><input name="siteName" class="input"></div><div class="field"><label>Program name</label><input name="programName" class="input"></div><div class="field"><label>Bridge headline</label><input name="bridgeHeadline" class="input"></div><div class="field"><label>Bridge subheadline</label><textarea name="bridgeSubheadline" class="input" rows="3"></textarea></div><div class="field"><label>Premium entry (POL)</label><input name="premiumEntryPol" class="input" type="number"></div><div class="field"><label>RM dApp referral base URL</label><input name="dappReferralBaseUrl" class="input" placeholder="https://app.thermcircle.com?ref="></div><div class="field"><label>BeMob postback URL (paid traffic)</label><input name="bemobPostbackUrl" class="input" placeholder="https://xxxxx.bemobtrcks.com/postback"></div><div class="field"><label>Telegram/support URL (optional)</label><input name="telegramUrl" class="input"></div><div class="field"><label>Support message</label><textarea name="supportLabel" class="input" rows="3"></textarea></div><label style="text-transform:none;letter-spacing:0;margin:10px 0"><input type="checkbox" name="showSponsorName"> Show sponsor name publicly</label><label style="text-transform:none;letter-spacing:0;margin:10px 0"><input type="checkbox" name="showQueueProgress"> Show number waiting in queue</label><button class="btn btn-primary" style="width:100%;margin-top:8px">Save Settings</button></form></div></div></div></section>
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