Add ORM query autocomplete inside .filter() / .exclude() / .annotate()

[FROWNINGdev]

This is the moat feature identified in competitor analysis: no shipped Django extension does ORM query autocomplete well.

Goal: when the user types inside Post.objects.filter(...), complete field names based on the parsed model index, and resolve lookups like author__name through FK edges.

Design sketch:

1. Detect .filter( / .exclude( / .annotate( call inside a Python file via lightweight regex or textDocument context.
2. Resolve the QuerySet's base model from the assignment chain (best-effort).
3. Suggest field names + __lookup traversal from the parsed WorkspaceIndex.
4. Warn on typos with a diagnostic.

Prior art: the archived django-intellisense extension had a partial implementation worth studying.

Bigger feature — likely v0.5+. Design discussion welcome on Discussions first.