docs(P03): full-stack examples — 5 jobspecs + rendered artifacts + walkthrough

P03 — full-stack example with ingress configured (REQ-094; gate C-20).

examples/full-stack/:
- web-app.md: kind Service, process runtime, 3 replicas, Unix socket
  (default R-007), rolling update, constraints (node.role==web),
  affinity (zone==a weight 80), lifecycle hooks (post_start/pre_stop).
- api.md: kind Service, process runtime, 2 replicas, TCP opt-in
  (service.bind: 127.0.0.1, R-007), canary update with manual promote,
  constraints (node.role==api, node.cpus>=2), env vars.
- worker.md: kind Job, process runtime, one-shot, timeout 300s, env
  vars, lifecycle hooks (register/drain).
- log-shipper.md: kind Service (DaemonSet workaround — parser gap),
  process runtime, constraints (node.role==logs), env vars. Notes the
  v0.9 parser gap (schedule: block not wired) in a callout.
- postgres.md: kind Service, process runtime, 1 replica, blue-green
  update, volumes with replication (replicate:peer-b,peer-c via
  Syncthing), constraints (node.role==db, node.cpus>=4, node.memory>=8192).
- rendered/: Traefik dynamic YAML (web-app, api) + systemd units
  (web-app, api, log-shipper) showing what Orca generates on target nodes.
- README.md: end-to-end walkthrough (init -> node join -> capacity set
  -> ns create -> job run -> list --watch -> inspect rendered -> verify
  ingress -> drain/rollback). Cross-links to docs/ingress.md.
- examples_test.go: Go test that parses + validates all 5 jobspecs
  against the current parser and schema validators (gate C-20).

All 5 jobspecs pass jobspec.ParseFile + schema.ValidatorFor(kind).

---ci---
project: orca
phase: 3
milestone: v0.10
status: execute
---/ci---

examples/full-stack/postgres.md

@@ -0,0 +1,48 @@
+---
+kind: Service
+name: postgres
+count: 1
+runtime:
+  one_of: process
+  command: /usr/lib/postgresql/16/bin/postgres -D /var/lib/postgresql/data
+ports:
+  - name: pg
+    port: 5432
+restart:
+  mode: service
+  attempts: 5
+  delay: 10s
+update:
+  strategy: blue-green
+  min_healthy_time: 60s
+  healthy_deadline: 10m
+service:
+  name: postgres
+  port: 5432
+health:
+  check_type: http
+  interval: 15s
+  timeout: 5s
+  unhealthy_threshold: 3
+volumes:
+  - name: data
+    type: host
+    source: replicate:peer-b,peer-c
+    target: /var/lib/postgresql/data
+    read_only: false
+constraints:
+  - node.role == "db"
+  - node.cpus >= 4
+  - node.memory >= 8192
+env:
+  POSTGRES_DB: appdb
+  POSTGRES_USER: orca
+  PGDATA: /var/lib/postgresql/data
+---
+# PostgreSQL
+
+Database service with a single replica, blue-green update strategy,
+and volume replication via Syncthing (replicate:peer-b,peer-c). The
+data volume is replicated to two peers for fault tolerance. Health
+check on port 5432. Constraints require DB-role nodes with >= 4 vCPUs
+and >= 8 GiB memory.