Fix payload truncation, client-secret auth, run pagination, and add architecture diagram

[Rishabh4275]

Summary

This branch contains four commits that together fix a Purview API payload bug, correct the client-secret
action input wiring, cap workflow run pagination, and add a high-level architecture diagram to the setup
guide.

Commits

1. Fix truncation bug (9677245)

Fixes a payload truncation issue in src/api/purviewClient.ts where outbound Purview requests were being
cut off. Simplified the size-enforcement path so payloads are constructed and sent intact.

• src/api/purviewClient.ts
• dist/index.js (rebuilt)

2. Update client-secret to use correct parameter (13e5aed)

Wires the client-secret action input through correctly so client-secret authentication actually works
end-to-end.

• action.yml — declares the client-secret input
• src/validation/inputValidator.ts + tests — validation updated to match
• Instructions.md, README.md, sample/ — docs and sample workflow updated to reference the correct
  input name
• dist/index.js (rebuilt)

3. Max limit for finding the last run (450e549)

Caps the GitHub Actions run-history lookup in gitHubActionsRunner.ts so first-run detection doesn't
paginate unbounded against the Actions API.

• src/runner/gitHubActionsRunner.ts
• dist/index.js (rebuilt)

4. Add overall Image for Instructions.md (e20080f)

Adds an Architecture Overview section near the top of Instructions.md with a Mermaid flowchart LR
diagram (renders natively on GitHub) showing the three systems being wired together — GitHub (target
repo, workflow repo, action, org secrets, ruleset), Microsoft Entra ID (app registration), and
Microsoft Purview — plus a short bulleted recap of the four things a user configures across the guide
and a one-sentence runtime summary.

• Instructions.md

Why

• The truncation and client-secret fixes unblock real customers using client-secret auth against larger
  files.
• The pagination cap prevents excessive Actions API calls on long-lived repos.
• The architecture diagram gives new users a mental model of which systems talk to which before they're
  asked to create app registrations, secrets, and rulesets.

Test notes

• Existing inputValidator tests updated for the renamed parameter.
• dist/ rebuilt for each code change.
• Documentation-only commit (Initial Commit #4) requires no test changes.