feat: return-to-project redirects from create/edit forms

When creating or editing items from a project detail tab, users now
return to that project's tab instead of the entity's own page.
Edit links pass from_project param; forms include hidden field.
Reassigning to a different project redirects to the new project.
Decisions/meetings create from project context inserts junction rows.
File uploads from project context redirect back to project files tab.

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

templates/note_form.html

@@ -16,7 +16,8 @@
     {% if prefill_task_id is defined and prefill_task_id %}<input type="hidden" name="task_id" value="{{ prefill_task_id }}">{% endif %}
     {% if prefill_meeting_id is defined and prefill_meeting_id %}<input type="hidden" name="meeting_id" value="{{ prefill_meeting_id }}">{% endif %}
     {% if prefill_focus_id is defined and prefill_focus_id %}<input type="hidden" name="focus_id" value="{{ prefill_focus_id }}">{% endif %}
-    <div class="form-actions"><button type="submit" class="btn btn-primary">{{ 'Save' if item else 'Create' }}</button><a href="{{ '/focus/' ~ prefill_focus_id ~ '?tab=notes' if prefill_focus_id is defined and prefill_focus_id else ('/notes/' ~ item.id if item else '/notes') }}" class="btn btn-secondary">Cancel</a></div>
+    {% if from_project is defined and from_project %}<input type="hidden" name="from_project" value="{{ from_project }}">{% endif %}
+    <div class="form-actions"><button type="submit" class="btn btn-primary">{{ 'Save' if item else 'Create' }}</button><a href="{{ '/projects/' ~ from_project ~ '?tab=notes' if from_project is defined and from_project else ('/focus/' ~ prefill_focus_id ~ '?tab=notes' if prefill_focus_id is defined and prefill_focus_id else ('/projects/' ~ prefill_project_id ~ '?tab=notes' if prefill_project_id is defined and prefill_project_id and not item else ('/notes/' ~ item.id if item else '/notes'))) }}" class="btn btn-secondary">Cancel</a></div>
 </div>
 </form></div>
 {% endblock %}