Add structured JSON configuration variable replacement to IIS deploy (Phase 9)

Summary

Mirrors Octopus's Octopus.Features.JsonConfigurationVariables (StructuredConfigurationVariablesBehaviour.cs:13-35). Walks operator-specified JSON files, recurses the object structure, replaces leaf values whose path matches a Squid variable name. Supports both : (colon, .NET Core IConfiguration style) and . (dot, .NET Framework style) path separators.

Distinct from Phase 8 SubstituteInFiles:

• SubstituteInFiles = TEXT-level #{X} token replacement (any format)
• StructuredConfigurationVariables = STRUCTURE-AWARE leaf replacement (operator stores ConnectionStrings:Default as variable name; walker matches JSON path connectionStrings.default and replaces ONLY that leaf)

PS1 hook order matches Octopus pipeline: SubstituteInFiles → ConfigurationTransforms → ConfigurationVariables → StructuredConfigurationVariables → IIS configure.

What ships

Production (+105 LOC)

Change	Notes
2 new constants	StructuredConfigurationVariablesEnabled + Targets
Targets via base64	Newlines preserved for multi-glob list
Update-IISStructuredJsonConfiguration PS1	Recursive Walk-JsonReplace helper; both : and . path separators; arrays of primitives skipped (Phase 9 MVP)
ConvertTo-Json -Depth 32	Default depth of 2 truncates configs

Test code (+260 LOC, 6 new tests)

Tier	New	What
Drift detector	1	Function presence; both path separators; ordering AFTER ConfigurationVariables
Unit	1	Toggle + Targets in preamble (Targets via base64)
Real-host	4	Top-level leaf; nested via : (.NET Core); nested via . (.NET Framework); feature-disabled gate

Octopus alignment

• JSON-only Phase 9 MVP: Octopus also handles YAML/properties via separate parsers; deferred to 9.5
• Both path separators: matches Octopus's case-insensitive lookup against both forms
• Hook order: matches DeployPackageCommand.cs:118 (LAST among rewriters)

Cumulative state after Phase 9

• Unit: 70 → 72 (+2)
• Real-host: 50 → 54 (+4)
• Octopus feature surface: 7/8 complete — only Package Extraction (Phase 10) remains

Test plan

• dotnet test --filter FullyQualifiedName~IISDeploy on macOS — 72 unit tests green
• dotnet test --filter Category=IISDeployE2E on macOS — 54 real-host tests skip cleanly
• dotnet build 0 errors
• CI run on windows-latest

Out of scope

• Phase 9.5: YAML/properties structured config; array element replacement
• Phase 10: Package extraction (NuGet/Zip) — unblocks UI "Package installation directory" mode
• Phase 11: Custom installation directory + purge
• Phase 12: IIS cert auto-import + private-key ACL

Breaking-change risk

None.