Address TODO/FIXME markers in v5 codebase

## Summary

There are 10 TODO comments across the v5 codebase indicating deferred work, incomplete implementations, or unresolved design questions. These should be triaged and addressed before GA.

## TODO Inventory

| Location | TODO |
|----------|------|
| `src/Func/Commands/Setup/SetupRunner.cs:933` | Hardcoded stack package — should discover from workload metadata |
| `src/Func/Commands/Start/Initialization/StartInitializationState.cs:41` | Host env vars should move to proper host environment variable management |
| `src/Func/Commands/Start/Initialization/Steps/InstallHostWorkloadInitializationStep.cs:90` | Missing download progress reporting |
| `src/Func/Bundles/InstalledBundleScanner.cs:44` | Prerelease filter rule needs spec confirmation |
| `src/Func/Commands/Workload/WorkloadSearchCommand.cs:93` | `--skip`/`--take` paging UX not yet surfaced |
| `src/Func/Workloads/Catalog/WorkloadPackageNotFoundException.cs:10` | Needs UX-appropriate error messages |
| `src/Func/Commands/Start/Azurite/Orchestration/ManagedAzuriteOrchestrator.cs:117` | Mechanism needed to surface info beyond initialization |
| `src/Workloads/ExtensionBundles/DownloadDefaultBundle.targets:24` | Switch pack-time payload source from public CDN |
| `src/Workloads/Workers/Node/Workloads.Workers.Node.csproj:17` | Decouple from upstream worker's precise package layout |
| `src/Workloads/Workers/Python/Workloads.Workers.Python.csproj:21` | Decouple from upstream worker's precise package layout |

## Proposed Approach

Triage each TODO:
- **Resolve now** — if the fix is straightforward and blocks GA
- **Convert to issue** — if it represents significant work that can be tracked independently
- **Remove** — if the concern is no longer valid

## Acceptance Criteria

- [ ] Each TODO is triaged (resolved, converted to issue, or removed with rationale)
- [ ] No remaining TODOs that represent GA-blocking incomplete functionality

Start with the ten listed TODO locations, especially the C# command, initialization, bundle, workload, and project files, and review each marker in context. Triage every item as resolved, converted to a separate issue, or removed with rationale; confirm any specification questions before deciding. Done means each TODO has a recorded disposition and no remaining GA-blocking incomplete functionality.

Written by the indexing model from the issue text.