[Chore] Re-enable isort import sorting (pre-commit + sweep) #25

Context
A recent PR review pointed out imports aren’t consistently sorted, and isort enforcement appears disabled/misconfigured (see PR #22 thread: #22 (comment)).

Current state

• .pre-commit-config.yaml has the isort hook commented out.
• Ruff is configured but import sorting (I rules) is not enabled yet (there’s a TODO in pyproject.toml).
• pyproject.toml already contains a [tool.isort] config (including import section headings like # Standard/# Third-Party/# First-Party).

Goal
Make import sorting deterministic and enforced (pre-commit + CI), without mixing a large formatting sweep into functional PRs.

Proposed plan

1. Decide enforcement tool

   • Option A: enable isort via pre-commit (preferred if we want to preserve the import section headers as configured).
   • Option B: enable Ruff import sorting (I) instead (fewer tools, but won’t preserve section-header comments the same way).

2. Enable enforcement

   • Update .pre-commit-config.yaml to enable the chosen hook(s).
   • If using Ruff I, update Ruff config ([tool.ruff.lint] select) and verify settings.

3. One-time formatting sweep

   • Run the sorter across the repo and commit the result as a dedicated PR.

Acceptance criteria

• pre-commit run --all-files either fixes import order or fails when imports are out of order.
• CI (or documented local command) enforces the same behavior.
• Import grouping stays consistent with the project’s conventions.