docs: enhance getting-started, hardware, and project collection indexes

Adds onboarding decision tree to getting-started/README.md so users can
quickly identify the right setup command for their situation.

Adds hardware vision overview to hardware/README.md explaining the
Peripheral trait and supported board types.

Expands project/README.md with scope explanation describing the purpose
of project snapshots and how they relate to documentation maintenance.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

docs/project/README.md

@@ -8,6 +8,10 @@ Time-bound project status snapshots for planning documentation and operations wo
 
 ## Scope
 
-Use snapshots to understand changing PR/issue pressure and prioritize doc maintenance.
+Project snapshots are time-bound assessments of open PRs, issues, and documentation health. Use these to:
 
-For stable classification of docs intent, use [../docs-inventory.md](../docs-inventory.md).
+- Identify documentation gaps driven by feature work
+- Prioritize docs maintenance alongside code changes
+- Track evolving PR/issue pressure over time
+
+For stable documentation classification (not time-bound), use [docs-inventory.md](../docs-inventory.md).