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).

guides/placement.md

@@ -0,0 +1,92 @@
+# Placement guide — where should a new project live?
+
+Reference doc for the "where does this run, which model, what data layer?" question. It
+encodes two things: a stable **decision sequence** (rarely changes) and a set of
+**infrastructure facts** (go stale — keep them current). `/new-project` walks this against
+every new idea (`guides/new-project.md`, Phase 2); `how-i-work.md` points here so any
+session placing a project consults it rather than guessing.
+
+> ⚠️ **The infrastructure facts below are UNVERIFIED.** They were generated one-shot from
+> chat history and have **not** been confirmed against the actual setup. Treat every fact in
+> the next section as provisional until reviewed and corrected with the user — see the
+> standards `ROADMAP.md` item "Verify & correct the placement guide." The *decision sequence*
+> and the *substance rule* are sound regardless; it's the specific service/model/network
+> facts that need a pass.
+
+## Infrastructure facts (PROVISIONAL — last generated June 2026, not yet verified)
+
+**Start9 server** — StartOS 0.4.x. Hosts long-running services as s9pk packages or plain
+containers. Believed running: Gitea (version control for LLM-assisted projects — the default
+repo home), Nextcloud (general file backup), Home Assistant (Container install), Electrs,
+Core Lightning + RTL, Open WebUI as the sovereign chat/session layer.
+
+**Inference** — Two NVIDIA DGX Sparks behind the Spark Control HTTP gateway on the LAN,
+serving Qwen3 (vLLM, OpenAI-compatible endpoints) as the primary production backend. Kokoro
+for TTS. bge-m3 for embeddings. Treated as real production capacity — existing apps (call
+transcription/recap, CRM pipeline, email-summary agent) already depend on it.
+
+**Data layer defaults** — SQLite for structured data; Qdrant + bge-m3 when semantic
+retrieval is needed; flat files when that's the honest answer.
+
+**Sovereignty boundary (standing rule)** — Anything touching sensitive investor, LP, or
+portfolio data uses local models only, via the Spark gateway. Frontier APIs (Anthropic etc.)
+are fine for everything else. Non-negotiable per project; the only question is which side of
+the line the project's data sits on.
+
+**Access** — WireGuard split-tunnel from macOS to the home subnet (runs alongside Proton
+VPN). iOS is constrained to a single VPN tunnel; workarounds are Tor onion addresses or a
+merged WireGuard config. So "reachable from phone" is a real design constraint, not a
+footnote.
+
+**Dev machine** — macOS with Claude Code. One-off and personal CLI tools live here happily.
+
+## Decision sequence (stable)
+
+Walk these in order; each answer narrows the next.
+
+**1. Sensitivity.** Does the project ingest, store, or send investor/LP/portfolio data to a
+model? If yes: local inference mandatory, hosting on the home subnet strongly preferred, and
+AGENTS.md must state the constraint explicitly so a coding session never "helpfully" wires in
+a frontier API call with payload data.
+
+**2. Runtime shape.** One-shot CLI / scheduled job / long-running service / interactive UI?
+- One-shot or personal CLI → Mac. Don't deploy what doesn't need deploying.
+- Scheduled job → Mac launchd if it only matters while the laptop lives; Start9 if it must
+  run unattended 24/7.
+- Long-running service, or anything other devices/family/agents need to reach → Start9.
+
+**3. If Start9: s9pk or plain container?** s9pk earns its packaging cost when the service
+wants the StartOS lifecycle — backups, health checks, dependency management, clean updates —
+or could plausibly be published for others. Plain container (or script) wins for experiments,
+single-user glue, and anything still changing shape weekly. Default for prototypes: container
+now, promote to s9pk if it survives and stabilizes. Packaging for 0.4.x is nontrivial; don't
+pay it on spec.
+
+**4. Model routing.** Default to local Qwen3 via the Spark gateway when the sovereignty
+boundary applies, when latency/cost favor local, or when the task is well within Qwen3's
+capability. Route to frontier (Claude API) for hard reasoning on non-sensitive data. Record
+the chosen endpoint in AGENTS.md so sessions don't guess.
+
+**5. Data layer.** SQLite unless there's a reason; Qdrant + bge-m3 when retrieval quality is
+the product; flat files for logs and artifacts. Name Qdrant collections per-project to avoid
+the shared-collection mess.
+
+**6. Interface.** CLI first unless the UI *is* the product. If it must be reachable from the
+phone, remember the iOS single-tunnel constraint — decide up front whether that means onion
+address, merged WireGuard config, or "Mac-only is fine."
+
+**7. Repo home.** Gitea on Start9. Always — even for parked-then-revived ideas, so history
+accumulates in one place.
+
+## Phase-exit criteria — the substance rule
+
+Phase exits are falsifiable substance: numbers and demonstrable behavior. "46/46 tests
+pass," "recap generated from a real 40-minute call in under 2 minutes," "correct doc in
+top-3 for 9/10 canned queries." If the criterion can't fail, it isn't a criterion.
+
+## Maintenance
+
+The **infrastructure facts** section is the part that goes stale. When the infra changes —
+new hardware, StartOS version, model lineup, network setup, a service added or retired —
+update that section here rather than working around it in conversation. The decision sequence
+and the substance rule rarely change.