story/suggestion form: match title length in db

This bug has existed since before the site launch, the model and form have never
agreed. The bookmarklet (introduced in 41b6d76) prefills the title field without
awareness of the maximum title length. The model has a limit of 150 (95b4906)
but the form field has a limit of 100 (093747b). Browsers limit text input but
don't prevent form submission and show an error only when the field is focused
(if they show one at all, Safari). The prod db has 379 stories with titles > 100
bytes. Also, SQL databases enforce length as bytes and Rails validates length as
characters, argh. So one more thing that's never been right is
https://web.archive.org/web/20051212105833/http://www.loudthinking.com/arc/000516.html

app/models/story.rb

@@ -1017,6 +1017,12 @@ def fetched_attributes
     end
   end
 
+  def self.title_maximum_length
+    validators_on(:title)
+      .sole { |v| v.is_a? ActiveRecord::Validations::LengthValidator }
+      .options[:maximum]
+  end
+
   private
 
   def valid_canonical_uri?(url)

app/views/stories/_form.html.erb

@@ -20,7 +20,7 @@
 
   <div class="boxline">
     <%= f.label :title, "Title:", :class => "required" %>
-    <%= f.text_field :title, :maxlength => 100 %>
+    <%= f.text_field :title, maxlength: Story.title_maximum_length %>
     <p class="actions title-reminder">
       Please remove extraneous components from titles such as the name of the site, blog, section, and author.
       <span class="title-reminder-thanks">