Use oxlint and prettier for linting and formatting

[BowTiedRadone]

This PR adds linting and formatting to Rendezvous. oxlint enforces correctness, suspicious code, performance, and style rules, while prettier with @trivago/prettier-plugin-sort-imports handles code formatting and import ordering.

Key additions

• oxlint linter with tuned rule categories (correctness, suspicious, perf, style) and project-specific overrides
• prettier formatter with sorted imports
• CI pipeline: fmt-lint job runs first as a gate for other jobs
• Codebase-wide fixes: shadowed declarations, consistent type definitions (type over interface), arrow function expressions, Record<K, V> over index signatures, required params before optional

New scripts

• lint: run oxlint
• lint:fix: run oxlint and fix (applicable for rules that can be fixed automatically)
• fmt: run prettier
• fmt:check: check formatting without writing

Closes #194.

[BowTiedRadone]

What's left here is to carefully go over the currently disabled linting rules and re-enable the low noise/high value ones.

[wileyj]

this is definitely linted! seems fine, and tests are all passing