chore(cardshed): bootstrap @lab/ll-CARDSHED stack contract

[w7-mgfcode]

Why

The CARD SHED deterministic core (PRP 2) landed in #139/#140 at @lab/ll-CARDSHED/apps/core/, but the stack lacks a W7-Base contract root:

• No .w7-meta, compose.yml, .env.example, .gitignore at @lab/ll-CARDSHED/
• No README.md, CLAUDE.md, AGENTS.md, BLUEPRINT.md
• No stack-local rules (.claude/rules/)
• No .stitch/DESIGN.md placeholder (PRP 3 M1 will populate)

Per .shared/W7-CONTRACT.md, every stack one level deep inside a zone needs the contract artifacts. Today cardshed is just a TypeScript library floating under apps/core/ — it's not discoverable via w7 stat and it's not legible to future contributors landing on the repo.

What ships (this PR)

Stack root scaffolding modeled on @lab/ll-RELIQUARY/:

• README.md — human-facing overview, status, stack tech, quickstart
• CLAUDE.md — Claude-side project rules (mirrors RELIQUARY shape, cardshed-specific)
• AGENTS.md — agent-side overview
• BLUEPRINT.md — index pointing to PRPs/cardshed-{01,02,03}-*.md as source-of-truth
• .w7-meta — minimal, declares "boilerplate; no live services yet"
• compose.yml — stub (alpine sleep) so the stack is discoverable; replaced at PRP 3 M1
• .env.example — placeholder (real env arrives with apps/ui/)
• .gitignore — adapted from RELIQUARY
• .claude/rules/ui-design-pipeline.md — stack-local mandatory UI pipeline (mirrors RELIQUARY)
• .claude/rules/core-determinism.md — stack-local rule encoding PRP 2's purity guarantees
• .stitch/DESIGN.md — placeholder for PRP 3 M1
• data/.gitkeep, dogfood-output/.gitkeep, docs/SCREENS/.gitkeep, docs/DECISIONS/.gitkeep

Out of scope

• apps/ui/, apps/server/ scaffolding (PRP 3 M1+)
• Stitch generation of the actual design system (PRP 3 M1)
• Any rules-engine or core changes (PRP 2 is sealed)
• Updating root README.md active-stacks table (separate PR — same gap exists for RELIQUARY)

Acceptance

• @lab/ll-CARDSHED/.w7-meta parses; docker compose --env-file .env.example -f @lab/ll-CARDSHED/compose.yml config -q exits 0
• All three policy scripts (prod-privileged, prod-no-root-mount, zone-ingress-naming) still exit 0
• Commit message uses chore(cardshed): ... per .claude/rules/commit-format.md
• No compose.yml privileged: or host root mounts (we're in @lab, but the policy still applies as a stack-shape sanity check)

Reference

• @lab/ll-RELIQUARY/ — template
• .shared/W7-CONTRACT.md — schema
• PRPs/cardshed-01-blueprint.md — tech-stack decision
• PRPs/cardshed-02-core-prp.md — already shipped (feat(cardshed): bootstrap CARD SHED deterministic core rules engine #139)
• PRPs/cardshed-03-experience-prp.md — next slice after this lands