fix(P06): workloadToTaskSpecs command split + runnable examples

Root cause: orca job run <example>.md failed with fork/exec: no such
file or directory on every example. Two compounding problems:

1. workloadToTaskSpecs (internal/cli/job.go:340) passed the entire
   runtime.command string (e.g. "/usr/bin/httpd -f /etc/orca/web-app/
   httpd.conf") as a single binary path to exec.Command, which then
   looked for a file literally named "/usr/bin/httpd -f ..." and
   failed. The v0.9 markdown parser stores command: as a raw string;
   the legacy HCL path had separate command+args fields. Fix: add
   splitCommand helper that splits on strings.Fields into binary+args,
   with /bin/true fallback for empty commands.

2. The example commands referenced binaries that don't exist on a bare
   Linux machine (/usr/bin/httpd, postgres, api-server, fluent-bit).
   Fix: rewrite the 5 example runtime.command values to use /bin/sleep
   3600 (long-running services) or /bin/echo (one-shot job) so they
   run out-of-the-box. Each file has a Production substitution note
   showing the real binary to use in deployment.

Verified: orca job run examples/full-stack/worker.md now succeeds
(exit 0). All 4 services (web-app, api, log-shipper, postgres) start
correctly (task started, pid assigned). 12 new unit tests pass
(splitCommand: 7 cases, workloadToTaskSpecs: 5 cases). All 5 example
jobspecs still parse + validate (gate C-20). make lint clean.

---ci---
project: orca
phase: 6
milestone: v0.10
status: execute
decisions:
  - id: D-195
    decision: split command string via strings.Fields in workloadToTaskSpecs
    rationale: exec.Command expects binary path + args as separate elements;
      the v0.9 markdown parser stores command: as a single string with no
      args field (unlike legacy HCL). strings.Fields is dep-free and handles
      multiple spaces/tabs. Shell quoting (single/double quotes inside the
      command) is not handled — examples avoid sh -c with quoted strings.
    confidence: 0.95
    alternatives: [shellquote.Split from mvdan/sh (adds dependency)]
lessons:
  - The v0.9 markdown jobspec path needs the same command+args split that
    the legacy HCL path had via separate command/args fields. The parser
    stores command: as a raw string; the CLI must split it before passing
    to exec.Command.
  - Example jobspecs should use /bin/sleep and /bin/echo (binaries that
    exist on every Linux machine) so they run out-of-the-box. Descriptive
    production commands belong in a comment block, not in runtime.command.
---/ci---

examples/full-stack/rendered/systemd-api.service

@@ -3,7 +3,7 @@
 # Path on target node: /etc/systemd/system/orca-v1-api.service
 # service.bind: 127.0.0.1 (TCP opt-in, R-007)
 [Service]
-ExecStart=/usr/bin/api-server --listen 127.0.0.1:9090
+ExecStart=/bin/sleep 3600
 RuntimeDirectory=orca/alloc-api-0
 # socket: /run/orca/alloc-api-0/port-api.sock
 ExecStartPre=/bin/echo orca: bind 127.0.0.1 port api (tcp, R-007 opt-in)

examples/full-stack/rendered/systemd-log-shipper.service

@@ -2,6 +2,6 @@
 # Generated by SystemdEmitter (internal/emitter/systemd.go)
 # Path on target node: /etc/systemd/system/orca-v1-log-shipper.service
 [Service]
-ExecStart=/usr/bin/fluent-bit -c /etc/orca/log-shipper/fluent-bit.conf
+ExecStart=/bin/sleep 3600
 RuntimeDirectory=orca/alloc-log-shipper-0
 # socket: /run/orca/alloc-log-shipper-0/port-metrics.sock

examples/full-stack/rendered/systemd-web-app.service

@@ -3,9 +3,9 @@
 # Path on target node: /etc/systemd/system/orca-v1-web-app.service
 # Unit name prefix orca-v1- (dual-write window, REQ-090)
 [Service]
-ExecStart=/usr/bin/httpd -f /etc/orca/web-app/httpd.conf
-ExecStartPost=/usr/local/bin/warm-cache.sh
-ExecStop=/bin/sh -c 'sleep 5'
-ExecStop=/usr/local/bin/drain.sh
+ExecStart=/bin/sleep 3600
+ExecStartPost=/bin/echo cache warmed
+ExecStop=/bin/sleep 5
+ExecStop=/bin/echo draining web-app
 RuntimeDirectory=orca/alloc-web-app-0
 # socket: /run/orca/alloc-web-app-0/port-http.sock