feat(project-bootstrap): add we're on Windows to default CLAUDE.md template

Pin every newly-bootstrapped project to Windows / PowerShell out of the box
by adding a fifth trigger line to the CLAUDE.md template. The line activates
the active-platform skill, which then governs all command/example output.

- skills/project-bootstrap/assets/CLAUDE.md.template: append `we're on Windows`
- skills/project-bootstrap/SKILL.md: sync the embedded preview in Step 5 and
  document the Linux/macOS substitution
- CLAUDE.md (this repo): backfill the line — was created from old template
- dist/project-bootstrap.skill: rebuilt
- .wiki/source/active-platform-decision.md: append "Wired into project-bootstrap"

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

skills/project-bootstrap/SKILL.md

@@ -161,8 +161,14 @@ talk like a caveman
 use superpowers
 use project wiki
 use task management system
+we're on Windows
 ```
 
+The `we're on Windows` line activates the `active-platform` skill and pins the
+project's default platform to Windows / PowerShell — so generated commands and
+README quick-starts use PS-native syntax. Bootstrapping on a Linux or macOS
+host? Substitute `we're on Linux` or `we're on macOS` instead.
+
 ---
 
 ## Step 6 — Commit