fix(job_key): hash the URL alone so a re-listed non-Latin title keeps one key (#502)

* fix(job_key): hash the URL alone so a re-listed non-Latin title keeps one key

* docs(changelog): record the job_key URL-identity fix

Adds the [Unreleased] / Fixed entry for #501, naming tools/job_key.py and
tests/test_job_key_url_identity.py.

The entry states the migration consequence in bold: an entry written before
this fix, for a non-Latin title on a portal without a numeric id, re-keys once
on the next scrape. It also names where those entries surface,
keys_not_matching_current_rule, and that --audit never rewrites them.

Verified that claim rather than asserting it. A seen_jobs.json holding one
entry under its pre-fix key for a Cyrillic-titled freehire URL reports
keys_not_matching_current_rule: 1 under the fixed audit. The same audit over a
real 884-entry seen_jobs.json reports 0, because those keys are the
company_title form that is_canonical() excludes from the drift check.

tests/test_job_key.py

@@ -70,6 +70,35 @@ class MakeKey(unittest.TestCase):
         self.assertTrue(is_canonical(key))
         self.assertFalse(key.startswith("_"))
 
+    def test_one_url_keeps_one_key_when_a_non_latin_title_is_re_listed(self):
+        # freehire is the shipped multi-market portal, and its public API
+        # returns Cyrillic and Greek titles. Its real slugs carry no run of six
+        # digits, so the numeric-id branch above never fires for them and the
+        # hash is the only key half left. Hashing the title alongside the URL
+        # made that hash move whenever a portal re-listed the same posting with
+        # the title altered - including a mere case change, which this portal
+        # really does emit ("Инженер" and "инженер" both appear).
+        #
+        # URL and slug are real values from freehire's public API, not
+        # constructed: https://freehire.me/api/v1/agent/jobs/search?q=инженер
+        url = "https://freehire.me/jobs/inzhener-ooo-chen-hlk3qjfg"
+        company = "ООО Чен"
+        first = make_key(company, "Инженер", url=url)
+        recased = make_key(company, "инженер", url=url)
+        retitled = make_key(company, "Инженер-механик", url=url)
+        self.assertTrue(is_canonical(first))
+        self.assertEqual(first, recased)
+        self.assertEqual(first, retitled)
+
+    def test_distinct_urls_still_get_distinct_keys(self):
+        # The counterpart to the above: collapsing title variants must not
+        # collapse two genuinely different postings from one company. Both
+        # slugs are real freehire values.
+        company = "ООО Чен"
+        a = make_key(company, "Инженер", url="https://freehire.me/jobs/inzhener-ooo-chen-hlk3qjfg")
+        b = make_key(company, "Инженер", url="https://freehire.me/jobs/inzhener-mup-g-khabarovska-tep")
+        self.assertNotEqual(a, b)
+
 
 class CompanyFallbackCLI(unittest.TestCase):
     def key_for(self, company, url="https://example.com/jobs/123456"):