feat: --quick economy preset for short, low-cost tests (CLI + REPL + web)

Billing concern: a full run with 2-3 voters, deep chaining and exhaustive recon
burns a lot of tokens. --quick is one switch for a fast, cheap pass:
one voter, one chain round, light recon (intensity 1), ≤6 agents, eco budget.
Dropping voting from 3 models to 1 is the biggest saver.

- CLI: --quick on run/whitebox/greybox (apply_quick, applied last so it wins)
- REPL: /quick (aliases /economy /eco), listed in help + completion
- web: ⚡ Quick-mode checkbox in the wizard -> /quick in the REPL script
- README: documented in the flags table
- 420 tests passing

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/public/index.html

@@ -221,6 +221,9 @@
             <div class="section-desc">Optional. Left on <em>unlimited</em>, the run behaves exactly as it always has — full depth, no cap.</div>
           </div>
           <div class="field-row">
+            <div class="check-row check-quick"><input type="checkbox" id="fieldQuick" /> <label for="fieldQuick"><b>⚡ Quick mode</b> — short, low-cost test</label>
+              <div class="field-help">Economy preset: 1 voter, 1 chain round, light recon, ≤6 agents, eco budget. The big token saver. Wins over the settings below.</div>
+            </div>
             <div class="field-group"><label class="field-label" for="fieldBudget">Budget mode</label>
               <select class="narrow" id="fieldBudget">
                 <option value="unlimited" selected>unlimited · full run (default)</option>