fix(lint): E402 is on — the ignore meant for main.py had let 11 late imports in elsewhere

ruff.toml ignored E402 everywhere for main.py's logging setup. Measured: 28 hits, of which 11
had nothing to do with it — runner.py's logger line between its imports, models.py importing
canonical_email mid-file, a test constant above its imports, and main.py's own third-party and
mimetypes imports. Those are moved up. What stays after configure_logging in main.py is marked
per statement (noqa E402, logging is configured first), its comment now says why the order
matters (a line logged while importing, not the logger's creation). The register row goes, the
ruff key whitelist loses ignore, and a late import is red again. The T20 comment counts the
third deliberate print (scripts/e2e_seed.py).

docs/gates.md

@@ -74,7 +74,6 @@ project checks needs a row.
 
 | Scope | Narrowed | Why | Measured |
 | --- | --- | --- | --- |
-| backend + scripts | `E402` — ignored | A few modules (`main.py`, `scripts/e2e_seed.py`) run setup — logging, `sys.path` — before their imports on purpose. | — |
 | backend + scripts | `B008` — narrowed: `fastapi.Depends`, `fastapi.Query` declared immutable | FastAPI's dependency injection IS a call in a default argument, on every route. Every other call in a default still fails. | 474 sites, all of them FastAPI |
 | backend/app | `C901` — not in ruff; measured by `tests/test_source_size.py` | Ruff has no per-function baseline, so turning it on would need a `noqa` per offender, and a `noqa` lets a function grow without limit. The test holds each offender, by name, at its current value. Tests and scripts are outside it: see the size / complexity rows under Lanes. | 32 functions over 10 |