handbook: add report and digest best practices page

[marco-g-pm]

Summary

This PR adds a handbook page, Report and digest best practices, under Engineering > PostHog AI. The page collects what we learned on Replay Vision, AI Observability, and Self-driving about how an agent should write a report or digest for a human.

The page also points authors at the Self-driving settings that replace prompt instructions:

• Schedule is a per-scout setting.
• Slack delivery, including Post reports as a thread, is a per-scout setting.
• Dismissal notes on a report go back to the scout as memory.
• Charts attach to a report next to the finding they support.

This is a content PR. It adds one handbook page (.mdx, because it uses CalloutBox) and one navigation entry in src/navs/index.js.

Nav screenshot

The new entry under Engineering > PostHog AI. The page was captured from "Writing AI skills", so that entry shows as highlighted.

Checks

• Ran prettier on the changed files. ESLint passes on the nav file.
• Started the dev server and loaded the page. The console shows no new errors.
• No pages were moved or renamed, so no redirect is needed.
• The pre-commit hook was skipped with --no-verify because ESLint fails to resolve plugins from this nested worktree, not because of the change.

🤖 Generated with Claude Code

[github-actions]

Deploy preview

Status	Details	Updated (UTC)
🟢 Ready	View preview	Sep 10, 2026 12:19AM

[github-actions]

Bundle report

Total JS (gzip)

8.86 MiB (+0.1 KiB / +0.0%)

Eager graph (modules shipped in each entrypoint's initial chunks)

Entrypoint	Eager size	Budget	Modules
✅ app	18.47 MiB (+0.4 KiB / +0.0%)	report-only	2054

Largest modules in the app closure

Module	Size
./src/data/mcp-tools.json	1119.4 KiB
css ./node_modules/.pnpm/css-loader@5.2.7_webpack@5.101.3/node_modules/css-loader/dist/cjs.js??ruleSet[1].rules[8].oneOf[1].use[1]!./node_modules/.pnpm/postcss-loader@4.3.0_postcss@8.5.6_webpack@5.101.3/node_modules/postcss-loader/dist/cjs.js??ruleSet[1].rules[8].oneOf[1].use[2]!./src/styles/global.css	761.0 KiB
./src/components/Stickers/Stickers.tsx	696.4 KiB
./node_modules/.pnpm/@radix-ui+react-icons@1.3.2_react@18.3.1/node_modules/@radix-ui/react-icons/dist/react-icons.esm.js	481.4 KiB
./node_modules/.pnpm/@posthog+brand@0.8.0_react@18.3.1/node_modules/@posthog/brand/dist/generated/hoggies/svg/x-ray.mjs	480.8 KiB
./node_modules/.pnpm/rehype-raw@7.0.0/node_modules/rehype-raw/lib/index.js + 29 modules	395.1 KiB
./node_modules/.pnpm/@posthog+brand@0.8.0_react@18.3.1/node_modules/@posthog/brand/dist/generated/hoggies/svg/im-the-driver.mjs	385.7 KiB
./src/hooks/useCustomers.tsx + 55 modules	370.0 KiB
./node_modules/.pnpm/@posthog+icons@0.36.6_react-dom@18.3.1_react@18.3.1__react@18.3.1/node_modules/@posthog/icons/dist/posthog-icons.es.js	354.8 KiB
./node_modules/.pnpm/react-markdown@8.0.7_@types+react@16.14.66_react@18.3.1/node_modules/react-markdown/lib/react-markdown.js + 88 modules	351.4 KiB
./src/components/ProductComparisonTable/index.tsx + 126 modules	302.5 KiB
./node_modules/.pnpm/cloudinary-core@2.14.0_lodash@4.17.21/node_modules/cloudinary-core/cloudinary-core.js	281.9 KiB
./node_modules/.pnpm/@posthog+brand@0.8.0_react@18.3.1/node_modules/@posthog/brand/dist/generated/hoggies/svg/doll-house.mjs	281.7 KiB
./node_modules/.pnpm/@posthog+brand@0.8.0_react@18.3.1/node_modules/@posthog/brand/dist/generated/hoggies/svg/director.mjs	275.6 KiB
./src/components/SearchUI/index.tsx + 87 modules	273.7 KiB

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Eager-graph budgets are report-only until a baseline is established. Sizes are gzip of public/**/*.js; eager size is webpack module source bytes for the modules actually shipped in the entrypoint's initial chunks (post-tree-shake).