fix(feedback): enforce anonymous submissions

[nwparker]

Summary

• make feedback anonymity an explicit IPC flag and allow-list the backend POST body
• remove anonymous contact fields so checked anonymous never sends identity/contact data upstream
• add regression coverage for stale identity/contact fields in anonymous feedback payloads
• unblock current oxlint config parsing and replace the rich markdown boundary reset with derived state so full lint can run

Verification

• pnpm exec vitest run --config config/vitest.config.ts src/main/ipc/feedback.test.ts
• pnpm run tc:node
• pnpm run tc:web
• pnpm lint
• pnpm exec oxfmt --check .oxlintrc.json src/main/ipc/feedback.ts src/main/ipc/feedback.test.ts src/preload/index.ts src/preload/api-types.ts src/renderer/src/components/sidebar/SidebarToolbar.tsx src/renderer/src/components/editor/RichMarkdownErrorBoundary.tsx