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/prepare-action.test.js

@@ -23,6 +23,17 @@ test('URLs are validated and preserved whole, never shortened', () => {
   assert.equal(out.kind,'ready');
   assert.ok(new URL(out.url).searchParams.get('q').endsWith(source));
 });
+test('shortened selections end on a whole word and decode cleanly', () => {
+  assert.equal(typeof prepareAction, 'function');
+  const out=prepareAction(req({source:'lorem ipsum '.repeat(2000)}));
+  assert.equal(out.kind,'shortened');
+  const words=new URL(out.url).searchParams.get('q').replace('[Selected text shortened]','').trim().split(/\s+/);
+  assert.ok(words.length>1);
+  for (const word of words) assert.ok(word==='lorem'||word==='ipsum',`cut mid-word: ${word}`);
+  const emoji=prepareAction(req({source:'😀 '.repeat(9000)}));
+  assert.equal(emoji.kind,'shortened');
+  assert.doesNotThrow(()=>decodeURIComponent(new URL(emoji.url).search.slice(1)));
+});
 test('long selections preserve instructions, repetition and Unicode with explicit consent', () => {
   assert.equal(typeof prepareAction, 'function');
   const settings={...DEFAULT_SETTINGS,promptTemplate:'START {query} AGAIN {query} END',temporaryChat:true,webSearch:true};