build: switch to oxfmt and oxlint

[TheGreatAxios]

Closes CL-9379

Summary

• Stacked on fix(uploads): store upload bytes per version #31, the tip of the open stack, so the reformat covers every file on it
• Add oxfmt and oxlint as exact-pinned devDependencies (the repo had no formatter or linter)
• Run lint and format:check in the test workflow after install
• Remove the unused ArtifactDb type import from src/content-store.ts and an unused row binding in e2e/tools.test.ts (no-unused-vars)
• .oxfmtrc.json sets printWidth: 80 (Prettier's width); everything else is oxfmt's defaults, including sorting package.json keys
• .oxlintrc.json turns the correctness category from warn to error; no rules are disabled
• lint runs oxlint, format runs oxfmt, format:check runs oxfmt --check

Commits

1. build: switch to oxfmt and oxlint: tooling, configs and lint fixes
2. style: format with oxfmt: mechanical reformat only (28 files changed, 1487 insertions(+), 520 deletions(-)), safe to skip in review