Add frontend integration guide for IIS deploy step
Summary
534-line spec at `docs/iis-deploy-frontend.md` for SquidWeb engineers building the `Squid.DeployToIISWebSite` step UI. Mirrors Octopus's "Deploy to IIS" step layout 1:1 so operators carrying Octopus specs across to Squid see exactly what they expect.
Covers:
- 14 UI cards with conditional visibility rules
- Every action property: name, type, default, UI shape, validation, sensitivity
- Bindings JSON schema (HTTP / HTTPS / SNI variants)
- Variable reference primer (`#{X}` plain + `#{X | Filter}` 1.6.9 form)
- Two complete example payloads (minimal HTTP + production HTTPS + full rewriter pipeline)
- End-to-end UX checklist for FE implementation
- Backend-side property-consumption reference (where each property lands in the PS1)
Property surface authority pinned to `IISDeployProperties.cs` — drift detector keeps agent-side consumers in lockstep.
Filed under 1.7.0 because 1.6.9 milestone is already closed (release shipped); the doc describes 1.6.9 functionality but is added post-ship.
Test plan
-
Doc-only PR; no logic / test changes -
SquidWeb team review for clarity + completeness