Exclude Python virtualenvs from the Docker build context (#7658)

# Description of Changes

Stirling engine docker slimming

Exclude Python virtualenvs from the Docker build context
Drop unused provider SDKs from the engine dependency set
Retry the SQLite WAL switch when workers race on startup
Build the engine image in two stages and run it unprivileged
Swap voyage SDK for api call removing 200MB bloat
Bundle the AI engine in the fat image
Publish the AI engine as a standalone image


886MB to 295MB in docker file

And Docker fat is only 230MB bigger after adding (since it already has
python and some deps)

---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have run `task check` to verify linters, typechecks, and tests
pass
- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#7-testing)
for more details.

engine/tests/test_documents.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+from pathlib import Path
+
 import pytest
 
 from stirling.contracts import PageText
@@ -647,3 +649,19 @@ def _dummy_tool_def() -> object:
     """Sentinel passed to ``_prepare_search_knowledge``. The callback only inspects
     ``_search_count``; it doesn't read anything off the tool_def or context."""
     return object()
+
+
+# concurrent store startup
+
+
+def test_many_stores_open_the_same_file_without_locking_out(tmp_path: Path) -> None:
+    """Workers all construct a store against one file on boot; the WAL switch races."""
+    import concurrent.futures
+
+    db_path = tmp_path / "rag.db"
+    with concurrent.futures.ThreadPoolExecutor(max_workers=8) as pool:
+        stores = list(pool.map(lambda _: SqliteVecStore(db_path), range(8)))
+
+    assert len(stores) == 8
+    mode = stores[0]._conn.execute("PRAGMA journal_mode").fetchone()[0]
+    assert str(mode).lower() == "wal"