chore: dev tooling modernization (git-cliff, TS 6, ESLint 10, docs CI)

[jgs-jeeves]

Dev Tooling Modernization

Bring this repo in line with the current karmaniverous ecosystem standards.

Tasks

• Replace auto-changelog with git-cliff (remove auto-changelog dep, add cliff.toml, update release-it hooks if present)
• Upgrade TypeScript from 5.9.x to 6.x (resolve any breaking changes)
• Upgrade ESLint from 9.x to 10.x (migrate to flat config if still on legacy)
• Run ncu and upgrade remaining dev dependencies (review major bumps before applying)

Context

• git-cliff replaces auto-changelog across the ecosystem. Reference: repos already migrated include jeeves-watcher, jeeves-server, jeeves-meta.
• docs.yml from karmaniverous/gha-workflows automates TypeDoc → GitHub Pages deployment on push to main.
• TypeScript 6 and ESLint 10 are the current ecosystem baseline.