feat(home): multi-file upload + per-file analysis, drop tool grid

Home is now upload + analysis only. The page accepts multiple files in
one go, analyzes each independently, and renders findings grouped by
filename in bordered containers. The 3-section tool-card grid is gone —
discovery happens via the sidebar now.

Mechanics:
- file_uploader uses accept_multiple_files=True. Each file's findings
  cache in session_state["home_findings_by_file"] keyed by filename so
  removing a file via Streamlit's "x" button drops its findings too,
  and re-clicking Run only re-analyzes pending files.
- The first uploaded file is mirrored into the singular
  home_uploaded_{name,bytes,size} keys so tool pages continue to pick
  up an "active" upload through pickup_or_upload — no tool-page changes.
- New i18n keys: upload.intro_multi, upload.uploader_label_multi,
  upload.clear_results, upload.empty_state. upload.heading text is
  updated to "Upload one or more files to start" (EN + ES).

Dropped tests pinning the tool grid:
- TestHomeToolGridLocalization (test_chrome.py)
- test_home_tool_card_uses_es_name (test_smoke.py)
- TestLiteHomeGridBadges (test_lite_tier.py — locked-card lock-badge
  assertions; locking is still enforced per-tool-page via
  require_feature_or_render_upgrade)

2009 tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/gui/test_smoke.py

@@ -87,15 +87,6 @@ class TestHomePageRenders:
         text = collected_text(home_app)
         assert "Tus datos nunca salen" in text or "Se ejecuta localmente" in text
 
-    def test_home_tool_card_uses_es_name(self, home_app):
-        """When the home grid renders in Spanish, the dedup card title
-        must use the Spanish display name, not the English fallback."""
-        with_language(home_app, "es")
-        home_app.run()
-        text = collected_text(home_app)
-        assert "Buscar duplicados" in text
-
-
 class TestEveryPageRenders:
     """Parametrize over (page, language). Failure tells you exactly which
     page + which language broke."""