Add comprehensive documentation wiki for Docs Drift Guard

[devin-ai-integration]

Summary

Adds a full documentation wiki in docs/wiki/ with 15 Markdown pages covering every aspect of the Docs Drift Guard project. All content was derived from reading the README and source code — no application code was changed.

Pages added:

• Home.md — Index page with links to all wiki pages
• Getting-Started.md — Installation, setup, running the server
• Architecture-Overview.md — How the three guard layers work together (with ASCII diagram)
• Drift-Detection.md — Layer 1 deep dive: baseline → check → severity → artifacts
• Runtime-Call-Guard.md — Layer 2 deep dive: middleware behavior, audit log, observe-only design
• Contract-Tests.md — Layer 3 deep dive: all 8 test classes documented with what each test checks
• CLI-Reference.md — Full reference for baseline, check, audit commands with exit codes
• API-Endpoints.md — Complete API endpoint docs with request/response examples and seed data
• Slack-Notifications.md — Webhook setup, message structure, severity-specific behavior
• CI-CD-Integration.md — GitHub Actions workflow phases and severity handling
• Pre-Commit-Hooks.md — Installation, severity-based commit behavior, troubleshooting
• Demo-Walkthrough.md — Step-by-step guide for running the full demo
• Project-Structure.md — File layout with module-level descriptions
• Severity-Classification.md — GREEN/YELLOW/RED rules, exit codes, and automation behavior
• Troubleshooting.md — Common issues across server, CLI, hooks, CI, and Slack

Updates since initial commit

• Demo-Walkthrough.md: Fixed incorrect inline comment in the "Full Flow" script that said API uses "name" — corrected to API uses "first_name" + "last_name" (caught by Devin Review).

Review & Testing Checklist for Human

• Spot-check field names and schemas in API-Endpoints.md: These were written by reading app/main.py, not by running the API. Verify the documented request/response fields (especially for PATCH /v1/employees and POST /v1/employees) match the actual Pydantic models. The Demo-Walkthrough already had one incorrect field name — there may be others.
• Verify internal links work on GitHub: Navigate to docs/wiki/Home.md on the PR branch and click several cross-page links (e.g. [Drift Detection](Drift-Detection.md), [CLI Reference](CLI-Reference.md)) to confirm they resolve correctly within the docs/wiki/ directory.
• Cross-check exit codes in CLI-Reference.md: Verify exit codes 0, 1, 2, 3, 10, 11 against the actual logic in drift_guard/guard.py. An incorrect exit code in the docs could mislead CI/CD setup.
• Skim for tone/completeness: Ensure the docs match the team's expectations for developer-facing documentation and nothing important from the README was missed.

Suggested test plan: Browse docs/wiki/Home.md on the PR branch on GitHub, follow links to 3–4 pages, and compare a few specific claims (field names, exit codes, command syntax) against the source code.

Notes

• This is a docs-only PR — no application code, tests, or configuration files were modified.
• The wiki uses relative Markdown links between pages, which work when browsed from the docs/wiki/ directory on GitHub. They won't work as a GitHub Wiki (the built-in wiki feature) — they're repo-hosted docs.
• CI failure ("Detect API drift & contract violations") is pre-existing on main (PATCH 500 errors + schema bio field mismatch in contract tests) and unrelated to this PR. The check is not marked as required.
• Link to Devin run: https://app.devin.ai/sessions/521b2ec6fa2e4c319074825d96c1704b
• Requested by: @justinemach

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring