Fold idea-workshop into /new-project; add placement reference

Harvest the retired idea-workshop skill into the current new-project flow:
- form-factor gate (is this even a standalone repo, or a feature/skill/agent
  of something that exists? bail + reroute if so)
- worth-building gate at sign-off (build effort + ongoing tax -> BUILD/PARK/ADOPT)
- placement step that walks the new guides/placement.md
- falsifiable-exit substance rule and a posture section
- architectural decisions land in the new repo's AGENTS.md ## Decisions section,
  absorbing the old DECISIONS.md function (no separate ADR file)

Add guides/placement.md (ported from the skill) and point how-i-work.md at it.
Its infra facts are UNVERIFIED (one-shot from chat history) and flagged for a
review pass with me (ROADMAP item 7).

how-i-work.md

@@ -40,6 +40,7 @@ Universal preferences for any coding agent working with me, on any project. Load
 
 ## Building and releasing
 
+- **Placing a new project?** Where it runs (Mac vs my Start9), s9pk-vs-container, which model it routes to, its data layer, and its interface follow my standing infra conventions — consult `~/Projects/standards/guides/placement.md` (decision sequence + infra facts) rather than guessing.
 - **Bump the version before building an s9pk package.** For any project that is also a Start9 `s9pk` package, increment the package version (in the manifest) before running `make x86` or `make install`. This targets Start9 0.4.x: without a version bump my Start9 servers don't recognize the rebuilt package as updated, so the install silently does nothing. Bump first, then build and install.
 
 ## Maintaining instruction files (AGENTS.md, guides, this file)