build(docs): migrate to TypeScript 7

[praetordev]

Closes #316

Scope

• upgrade the documentation site from TypeScript 6.0.3 to 7.0.2
• replace Docusaurus 3.10.2’s incompatible published tsconfig with the equivalent TypeScript 7-compatible configuration already merged upstream
• remove the unused direct @docusaurus/tsconfig dependency
• document the compatibility decision, configuration-drift risk, and future return to the published config
• add a change-aware documentation CI gate so docs-site/** changes run only clean install, typecheck, and production build instead of silently skipping documentation validation

Required tests

• clean npm ci from the final lockfile
• npm run typecheck with TypeScript 7.0.2
• npm run build including Docusaurus MDX/link validation
• Node 22 development-server compilation
• HTTP 200 route smokes for /, /getting-started, and /concepts/execution-packs
• focused CI planner and workflow contract tests
• pinned actionlint
• complete ./scripts/verify-changed.sh local preflight: Go, UI, docs, database, deployment, product, and gosec gates passed

The documentation package does not define separate lint or unit-test scripts. TypeScript strict checking provides source/static validation, while the Docusaurus production build validates configuration, MDX, generated routes, and links.

Security and RBAC impact

Build-time documentation tooling only. No application runtime, authorization, or RBAC behavior changes. No compiler compatibility suppression is added; the removed baseUrl option and prior ignoreDeprecations setting are eliminated.

Dependencies

• follows the compatible Docusaurus patch update completed in Apply compatible documentation dependency patches #315
• mirrors the upstream Docusaurus TypeScript configuration change in break: require TypeScript >= 6.0 facebook/docusaurus#11915 until it is published
• Node 24 development startup OOM is a pre-existing issue that reproduces under both TypeScript 6 and 7 and is tracked separately in Fix Docusaurus development-server OOM on Node 24 #372; Node 22 development startup passes, while the production build passes under Node 24