Add a DevOps setup guide for the SharedServices deployment

[stefan-burke]

Adds docs/devops-sharedservices-setup.html — a self-contained HTML walkthrough of the one-time internal deployment setup, written for a DevOps engineer and whoever coordinates them (a contractor with limited access, per the constraint that started this).

What it covers:

• Who does what — a table splitting the steps by the access they need (infra access → platform DevOps, repo admin → whoever granted access, write access → the coordinator), so no tofu login is needed to make progress
• Step 1: Register the app in shared-services-infra — the static app spec values, links to the specs directory and PR-creation page, what tofu apply provisions, and the three outputs DevOps must hand back (deploy role ARN, bucket name, distribution ID)
• Step 2: Configure the sharedservices GitHub environment — exact variable/secret names with what each is for in plain terms (STATIC_PREFIX → S3 slot + URL path + build PATH_PREFIX; SITE_URL → canonical URLs with the no-trailing-slash rule; OIDC explained)
• Step 3: Dispatch the first deploy — what each workflow step does, including the guard, the build artifact, the --delete sync, and the CloudFront invalidation
• Step 4: Verify — an incognito/Okta gate check, deep links, internal search, feed URLs, canonical spot-check
• After the pilot — push-trigger enablement and the shared-workflow migration as follow-ups

Links throughout go to the actual pages needed (repo settings → environments, the workflow dispatch page, the infra specs directory, the platform's own static contract docs, #eng-team). README's SharedServices section now links to the file.

Verification: precommit gate green (lint, typecheck, code-quality, tests). Standalone file — no build system involvement, opens in any browser.