Add printer lifecycle fields and printer log

- Printer: bought_at, last_maintenance_at, decommissioned_at (all Date, nullable)
- PrinterLog: per-printer timestamped text entries (CASCADE delete)
- Migration 0003: adds columns + printer_logs table
- /printers/{id}: detail page showing lifecycle info + scrollable log
- POST /printers/{id}/log: add a log entry via modal form
- Printer names in list are now links to the detail page
- Add Printer modal includes optional purchase date

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/templates/printers.html

@@ -38,7 +38,7 @@
     <tbody>
     {% for p in printers %}
     <tr>
-      <td class="fw-medium text-white">{{ p.name }}</td>
+      <td><a href="/printers/{{ p.id }}" class="text-white text-decoration-none fw-medium">{{ p.name }}</a></td>
       <td class="text-secondary">{{ p.printer_type.name if p.printer_type else '—' }}</td>
       <td class="text-secondary small">
         {% if p.printer_type %}
@@ -96,6 +96,11 @@
                    placeholder="e.g. Workshop, Shelf 2">
           </div>
 
+          <div>
+            <label class="form-label text-secondary small">Purchase date</label>
+            <input type="date" name="bought_at" class="form-control bg-dark border-secondary text-white">
+          </div>
+
         </div>
         <div class="modal-footer border-secondary">
           <button type="button" class="btn btn-secondary btn-sm" data-bs-dismiss="modal">Cancel</button>