chore(backend)(deps): consolidate dependency updates

[berntpopp]

Summary

Consolidates backend dependency updates from #447 through #451 into one resolver-consistent change:

Dependency	Previous constraint/resolution	Updated constraint/resolution
pydantic-settings	>=2.14.2 / 2.14.2	>=2.15.0 / 2.15.0
deepdiff	>=6.7.0 / 9.0.0	>=9.1.0 / 9.1.0
oaklib	>=0.5.0 / 0.6.23	>=0.7.4 / 0.7.4
types-pyyaml	>=6.0.12.20260408	>=6.0.12.20260724
sqlalchemy[asyncio]	>=2.0.25 / 2.0.51	>=2.0.51 / 2.0.52
uvicorn[standard]	>=0.35.0 / 0.52.1	>=0.52.1 / 0.52.3

The unified uv resolution updates backend/uv.lock; both requirements exports are regenerated from that lock.

Resolver corrections

The standalone Dependabot patches in #447 and #449 edited generated requirements to versions that do not match the resolved lock:

• chardet remains at 5.2.0 because pronto==2.7.3 requires chardet<6, so 7.5.1 is unsatisfiable.
• pydantic-core remains at 2.46.4 because stable pydantic==2.13.4 requires that exact version; no production pre-release or resolver override is introduced.
• ast-serialize and librt remain at the versions selected by the current mypy graph.

Impact

No application code or API behavior changes. Backend dependency sources and generated exports are kept internally consistent, preventing the requirements-drift failures seen in #447 and #449.

Validation

• uv lock --directory backend --check
• make -C backend check-requirements-drift
• Ruff lint and format checks
• mypy: 234 source files, no issues
• Alembic upgrade against the dedicated PostgreSQL test database
• Python 3.12 backend suite: 1,863 passed, 16 skipped, 1 xfailed, 2 xpassed
• Coverage: 78.37% (70% required)
• Pre-commit hooks on all changed files

Supersedes #447, #448, #449, #450, and #451.