feat: scenarios for curator/memo-inbox/pi-grok, deploy and backup tooling

Scenarios
- memo-inbox: mirrored by copying; the live directory was not moved or modified
  and the service was not restarted. All four tracked files match byte for byte
  (pi-diff.sh reports SAME). Marked deploy = "mirror" so deploy-scenario.sh
  refuses --apply: applying a mirror would invert the direction of truth and
  could change a service in daily use.
- curator: target configuration, not yet deployed. .pi/SYSTEM.md replaces pi's
  coding-assistant prompt; durable role text is in .pi/APPEND_SYSTEM.md;
  profile.toml is the single source of truth for the launch contract.
- pi-grok: registered only. It is genuinely a coding agent, so the isolation
  baseline does not apply in full.

Corrections to the documentation, found by testing rather than by reading
- AGENTS.override.md does NOT block parent-directory context files; it only
  shadows its own directory. Verified: with an override file in the workspace, a
  marker in /tmp/AGENTS.md still reached the system prompt. The only effective
  switch is --no-context-files, so durable role text must live in
  .pi/APPEND_SYSTEM.md, which is a system-prompt file and unaffected by -nc.
  Verified end state: no coding-assistant framing, no pi-docs block, own
  identity and role text present, no parent pollution, only own skills/tools.
- PI_CODING_AGENT_DIR isolates settings/models/auth/trust/extensions/skills/
  prompts/themes under the agent directory -- stronger than the --no-* flags
  because it also repoints credentials -- but does NOT cover ~/.agents/skills.
  Measured: find-skills, modsearch and summarize still leak. So it complements
  --no-skills rather than replacing it.
- --append-system-prompt accepts a file path, which pi-grok relies on.
- cwd is what anchors .pi discovery: a probe that forgot cwd silently lost
  .pi/SYSTEM.md and kept the coding-assistant persona.

Tooling (all dry-run by default; none of them restarts a service)
- pi-diff.sh: compares tracked config against the live install in both
  directions, with a key-redacted comparison for models.json
- deploy-scenario.sh: installs a workspace and renders profile.toml into
  .pi/launch.json, then checks that every referenced path exists
- deploy-runtime.sh: renders models.json from its template, refusing placeholder
  or missing keys. Verified byte-identical to the live file
- pi-backup.sh / pi-restore.sh: archives outside the repo, sha256 manifest
  verified before any restore, live paths preserved rather than overwritten

Fixed while testing: pi-backup.sh compared the destination against the repo root
literally, so a relative --dest ./backups wrote credential archives into the work
tree. Now canonicalised with realpath; ./backups, an absolute in-repo path and
./docs/../backups are all refused.

docs/isolation-baseline.md

@@ -19,8 +19,8 @@ four independent layers. Use all four; each one covers a different failure mode.
 │   --no-prompt-templates / --no-themes / -nc / project trust  │
 ├──────────────────────────────────────────────────────────────┤
 │ L2 Personality  who the agent is                             │
-│   .pi/SYSTEM.md (replace) · APPEND_SYSTEM.md · AGENTS.md      │
-│   AGENTS.override.md · --system-prompt                        │
+│   .pi/SYSTEM.md (replace) · .pi/APPEND_SYSTEM.md · -nc        │
+│   AGENTS.md only if parent-dir layering is acceptable          │
 ├──────────────────────────────────────────────────────────────┤
 │ L3 Capability   which tools exist and are active             │
 │   --no-builtin-tools · --tools · --exclude-tools              │
@@ -142,8 +142,11 @@ capable, because the skill is finally reachable.
 2. **`env` discipline is the only secret boundary.** Without an explicit `env=`
    allowlist the node process inherits every `*_API_KEY` in the unit file.
 3. **Parent-directory context files.** Nothing prevents a future
-   `~/AGENTS.md` from layering into every scenario. Mitigate with `-nc` plus
-   `SYSTEM.md`, or an `AGENTS.override.md` in the workspace.
+   `~/AGENTS.md` from layering into every scenario, and `AGENTS.override.md`
+   does **not** prevent it -- it only shadows its own directory (verified: a
+   marker in `/tmp/AGENTS.md` still reached the prompt). The only effective
+   switch is `-nc`, which means durable role text must live in
+   `.pi/APPEND_SYSTEM.md` rather than `AGENTS.md`.
 4. **Workspace should be read-only to the service.** `--approve` trusts
    everything project-local, so a writable `.pi/` is a code-execution path.
    Enforce with systemd `ReadOnlyPaths=`.