Add slates doctor command

[devdattatalele]

Adds slates doctor — a workspace-wide consistency audit CLI.

Six checks across three severity buckets:

ERR  raw-throws       src/ contains throw new Error(...)
ERR  scope-file       OAuth integration without src/scopes.ts
ERR  vitest-config    test files present but no vitest.config.ts
WRN  contract-tests   src/auth.ts present but no *.contract.test.ts
WRN  zod-describe     Zod field declarations without .describe()
INF  readme           integration is missing a README.md

Filterable by --check and --integration, with --json for machine output. test-integrations/ excluded by default.

Useful for tracking codebase health and finding integrations that drift from the canonical Google-family conventions (gmail, google-meet, youtube, google-analytics).

README and 23 tests included.
@herber