refactor: remove the unused URL shortener

buildChatGptUrl and its fitToBudget helpers have had no production
caller since prepareAction took over routing; the 2026-10-05 plan kept
them only for existing tests until then. They also shortened silently,
against the ask-before-shortening rule, so they were a trap to reuse.

Port the tests that guard live code onto applyTemplate and
serializePrompt, including the $&, $`, $' and $$ regressions (checked to
fail against the string-replacement form), and cover prepareAction's
whole-word cut, which nothing tested before.

Also drop getContext's inputType password check. menus.OnClickData has
no inputType, so it never fired; Firefox already withholds password
fields from selectionText via mozIsTextField(true) in SelectionUtils
(bug 565717).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/actions.test.js

@@ -9,7 +9,6 @@ test('context prioritizes selection over link and excludes unrelated targets', (
   assert.deepEqual(actions.getContext({selectionText:' ',linkUrl:'https://example.com'}), {kind:'link',source:'https://example.com'});
   assert.equal(actions.getContext({mediaType:'image',pageUrl:'https://example.com'}), null);
   assert.equal(actions.getContext({editable:true,pageUrl:'https://example.com'}), null);
-  assert.equal(actions.getContext({selectionText:'secret',inputType:'password'}), null);
   assert.equal(actions.getContext({pageUrl:'https://example.com'}).kind, 'page');
 });
 test('selection actions and optional translation reflect settings', () => {