Phase 1 (rename DB) commit 1i: rename the SearchSpace table to workspaces
and flip all 24 inbound FK target strings (20 in db.py + the 4 satellite
models), plus the raw-SQL searchspaces references in the obsidian and
google-unification integration fixtures.
This completes the ORM half of Phase 1. The SearchSpace class name,
relationship/back_populates attribute names, and the /searchspaces API
route URLs are intentionally left for Phase 2.
Verified: unit 2375 passed/1 skip, integration 346 passed (baseline
parity); create_all builds every table with the workspaces name and all
FKs resolving to workspaces.id.
Phase 1 (rename DB) commit 1b: same attribute->physical column shim as
1a, applied to the document_files satellite model. ORM attribute name
unchanged; FK target string left for the searchspaces rename commit.
