Add optional annotations tab to ORCA design reference

[mryhmln]

Summary

• Add --annotations=<dir> flag to export-design-reference.js that loads field-level annotation YAML files
• Render an "Annotations" tab per schema with a program requirement matrix, source badges (system, applicant, derived, etc.), and expandable statute/notes details
• Feature is fully opt-in — without the flag, output is unchanged
• Remove unused global state selector UI (sidebar buttons, CSS, JS)
• Update ORCA intro to clarify OOUX/ORCA methodology
• Default active tab to "attributes" instead of "overview"
• Add unknown-argument rejection for the --annotations flag

Closes #128

How to validate

1. Check out the branch and install:

   git checkout feat/128-design-reference-annotations && npm install
   

2. Verify the script still works without annotations (no behavior change):

   node packages/contracts/scripts/export-design-reference.js \
     --spec=packages/contracts --out=/tmp/ref-test
   

   Open /tmp/ref-test/schema-reference.html — should render normally with no Annotations tab.

3. Verify annotations load when provided (create a test annotation file):

   mkdir -p /tmp/test-annotations
   cat > /tmp/test-annotations/application.yaml << 'YAML'
   schema: applications/Application
   fields:
     status:
       source: system
       programs:
         SNAP: required
         TANF: required
       statute: "7 CFR 273.2"
       notes: "Set automatically on submission"
   YAML
   
   node packages/contracts/scripts/export-design-reference.js \
     --spec=packages/contracts --out=/tmp/ref-test \
     --annotations=/tmp/test-annotations
   

   Open /tmp/ref-test/schema-reference.html, navigate to Application, and confirm the Annotations tab appears with the source badge and program matrix.

4. Run preflight:

   npm run preflight