chore(deps): upgrade major npm packages (Next 16, recharts 3, etc.)

[tembo]

Summary

Upgrades the major npm package versions in the interactions repo and fixes the breaking changes each one introduced. Build, type-check, and lint all pass, and the recharts-driven analytics chart was verified rendering in a real browser.

Major version bumps

Package	From	To
next	15.5.9	16.2.9
eslint-config-next	15.5.4	16.2.9
recharts	2.15.4	3.8.1
@vercel/analytics	1.5.0	2.0.1
lucide-react	0.503.0	1.21.0
sugar-high	0.9.3	1.2.1
tailwind-merge	2.6.0	3.6.0
@types/node	20.19.20	25.9.3
typescript	5.9.3	6.0.3

Breaking changes handled

• Next 16 removed the next lint command. The lint script now calls eslint . directly, and the legacy .eslintrc.json was migrated to a flat eslint.config.mjs (required by the modern ESLint pipeline) using eslint-config-next's native flat config export.
• Next 16 auto-applied two mandatory tsconfig.json changes during build (jsx: preserve → react-jsx, and adding .next/dev/types). Also removed the now-deprecated downlevelIteration flag (TypeScript 6 errors on it; it was a no-op at the project's ES2017 target).
• recharts 3 changed the custom-tooltip/legend content prop types. Updated components/ui/chart.tsx to the recharts-3 typing (DefaultTooltipContentProps / DefaultLegendContentProps, TooltipValueType), used a stable list key, and guarded the now-optional item.payload. The project's custom color tokens and styling were preserved.
• eslint-config-next 16 ships eslint-plugin-react-hooks v7 with React Compiler-aware rules. Fixed the newly-flagged issues:
  • shortcut-button/components/button.tsx: hoisted the handleClick useCallback above useHotkeys (was used before declaration) and added it to the hotkey deps.
  • content-timeline/page.tsx: replaced derived activeCheckpoint state + effect (setState in effect) with a useMemo computed during render.

Notably not upgraded

• ESLint stays on 9.x (^9.39.4). ESLint 10 is not yet viable: the plugins bundled by eslint-config-next (eslint-plugin-react, -import, -jsx-a11y) cap their peer range at ESLint 9, and ESLint 10 crashes eslint-plugin-react at runtime (contextOrFilename.getFilename is not a function). Bumped to the latest 9.x instead.

Verification

• pnpm build — passes (all 14 routes prerender)
• pnpm exec tsc --noEmit — passes
• pnpm lint — passes, 0 errors (2 pre-existing exhaustive-deps warnings left untouched as they predate this change and are behavior-sensitive)
• Ran the production server and confirmed the recharts 3 analytics chart renders (182 bars + axis labels) and pages return 200.

Note for reviewer

@types/node was bumped to the latest major (25) per the "upgrade majors" request, while the sandbox runs Node 22. This is harmless here but you may prefer to pin it to ^22 to match the runtime.

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Project	Deployment	Actions	Updated (UTC)
interactions-matter	Ready	Preview, Comment	Jun 18, 2026 5:10pm

[tembo]

Requesting review from @stylessh who has experience with the following files modified in this PR:

• package.json
• tsconfig.json
• .eslintrc.json
• pnpm-lock.yaml
• components/ui/chart.tsx
• app/(demos)/content-timeline/page.tsx
• app/(demos)/shortcut-button/components/button.tsx

[stylessh]

lgtm

[stylessh]

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