Fix Django/Wagtail search-bar parity bugs (container, wasmPath, Amazee trigger, per-page language)

[jeremyandrews]

Summary

Brings the Django adapter in line with the PHP adapters, fixing four issues surfaced by the GitMastery (demos/git-manual-django) demo. Each is paired with a regression test at the layer that would have caught it.

Fixes

1. Search UI mount (container) — {% scolta_search %} now emits a container CSS selector in window.scolta matching the rendered mount <div>. scolta.js auto-init reads it to locate its mount point; without it the markup rendered but the search box never did. (carried in from an earlier session; now under test)
2. wasmPath — now points at the full WASM glue module (…/wasm/scolta_core.js) rather than the containing directory, because scolta.js calls import(wasmPath) directly and a bare directory 404s. (carried in; now under test)
3. Amazee auto-provision trigger — maybe_auto_provision() now gates on no API key configured instead of ai_provider == 'amazee'. This mirrors the PHP adapters (ScoltaAiService::createClient lazy-provisions whenever getApiKeySource() === 'none'): a site with no key gets the free Amazee trial automatically; an explicit key always wins. Previously the default anthropic provider never provisioned and AI silently degraded.
4. Per-page language — SearchableMixin.to_searchable_content() derives the per-page filter language from a Wagtail locale (self.locale.language_code) when present, so multilingual sites populate the language facet per page instead of collapsing every page into the index's single bucket. Plain Django models without a locale keep the ContentItem default; explicit overrides must pass language= themselves (documented in the mixin).

Tests

• tests/test_search_browser.py (new) — browser-layer mount regression via Playwright; skips cleanly when chromium/playwright is absent. tests/browser_urls.py (new) serves the real assets.
• tests/test_adapter.py — container + wasmPath config guards.
• tests/test_amazee_django.py — key-gate trigger contract: default provider (anthropic) + no key + empty storage provisions; explicit key no-ops; already-stored creds no-op.
• tests/test_wagtail.py — Wagtail-locale language derivation; plain model keeps the default.
• tests/conftest.py — autouse fixture keeps AI-view tests hermetic now that "no key" triggers provisioning (the Amazee unit tests import the function directly and inject a fake client, so they're unaffected).
• CI: playwright install --with-deps chromium step added before the test run.

Testing done

• ruff check src tests clean; pytest 70 passed locally.
• Live-verified against the running demo (https://gitmastery-django.ddev.site/) on the editable package install:
  • / serves the search UI in main content, not the header; results render below the header band (no overlap).
  • Built index language filter map: {en: 286, es/fr/it/de: 285} (was {en: 1426}).
  • An English search returns zero /de//es//fr//it/ URLs; an Italian search from /it/ returns only /it/ URLs (auto language filter).
  • Health endpoint flips to ai_configured: true (provider anthropic → openai via the Amazee trial) after one search — the free trial provisions with no key set.