Standardise ruff configuration

[jonnyspicer]

Adds a lint.yml — this repo had no lint CI. Config lives in ruff.toml since there is no pyproject.toml. All 31 violations were auto-fixable.

Adopts a single ruff configuration across the org's Python repos. The config
is the one already in Tower-Finder/backend — the most considered in the org —
so this mostly spreads an existing standard rather than inventing one.

select = ["E", "W", "F", "I", "B", "UP", "S", "SIM"]   # 120 columns

with its documented ignore list (E501 and E402 as deliberate, B008 for
FastAPI's Depends(), the SIM readability rules, and the bandit exceptions).

Pinned to ruff==0.16.2. An unpinned ruff picks up new rules on release
and turns a green branch red without anything in the repo changing. Two repos
had floating constraints (ruff>=0.5, ruff>=0.8.0); both are now pinned.

Verification

Across the ten repos: 240 violations, 220 fixed by ruff --fix, 20 by hand.
Every repo reports All checks passed! under ruff 0.16.2, and every test suite
that runs was run and passes.

The hand fixes were real, not cosmetic — annotation == bool → is bool for
type identity, raise ... from e to preserve tracebacks, an unclosed file
handle, and unused loop variables. Where a flagged pattern was deliberate it
got a # noqa with a stated reason rather than a rewrite.

Note on conflicts

feat/gvl-metro-scoping is active across several of these repos. Import
reordering (I001) touches file headers, so expect conflicts there — taking
this branch's version of the import block is almost always right.

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