The previous commit only improved diagnostics — sources still returned
nothing. This commit makes them actually work.

glassdoor (upstream PRs speedyapply#347 + speedyapply#350):
- CSRF URL `/Job/computer-science-jobs.htm` 404s after the Next.js
  migration. Switch to homepage `/`, which reliably returns the
  embedded `"token":"..."` payload.
- `findPopularLocationAjax.htm?term=...` raw-interpolated locations
  with commas/spaces, causing HTTP 400 ("location not parsed"). Wrap
  the term in `urllib.parse.quote`. This was the actual root cause of
  every 0-row Glassdoor call — the city-only stripping in monitor's
  `run_search` only narrowed the pain, didn't fix it (Glassdoor still
  needs encoding even on bare city names with no comma).
- The `/graph` endpoint regularly returns 30 valid jobs alongside
  non-fatal `errors` on peripheral fields like `jobsPageSeoData`. Old
  code raised on ANY `errors` key and discarded everything. Only fail
  when `data.jobListings` is missing.
- `_get_location` now raises GlassdoorException with the underlying
  HTTP status code instead of returning `(None, None)` and losing
  context.
- Per-instance header dict so concurrent scrapes don't trample each
  other's CSRF token / UA, and so `_fetch_job_description` reads this
  scrape's token rather than whatever the most recent Glassdoor
  instance left in the module-global.

bayt:
- Slugify now folds accented Latin chars to ASCII before stripping
  non-ASCII (`ingénieur logiciel` → `ingenieur-logiciel` rather than
  `ingnieur-logiciel`).

google:
- The job-listing wrapper key (`520084652`) is a Google-internal
  function ID that gets rotated on redeploy; old parser failed
  immediately when it changed. Make the parser tolerate rotation:
  try the known keys first, then fall back to scanning every
  9-digit-key payload whose first record structurally matches a job
  shape (title/company/location strings + nested URL list). Log the
  fallback key when it fires so we can bake it back into the known
  list.
- `find_job_info` (used by paginated responses) gets the same
  treatment — if no known key matches, walk the JSON looking for
  arrays whose first item shape-matches a job record.