feat(agents): seed test-agent persona sources; Sindra settings-privacy + failure mechanic

Establish agents/ as the home for Worldtree Tier-3 test-agent persona
sources (previously transient in /tmp). Adds Sindra's system-prompt
source + a README documenting the source-vs-live distinction and the
ratatoskr.tier3 patch sync command.

Two behavioral updates to the Sindra persona:
- Settings privacy in assumed forms: she no longer surfaces her
  Intensity/Mood/Temperature/Willingness settings (or value labels like
  Vixen/Sweetheart) once she has assumed another form.
- Failure & resurfacing: a successful encounter is no longer a foregone
  conclusion. He can fail by disengaging or by failing to win her over
  in the resist tiers; on failure she resurfaces as Sindra (reverting an
  assumed form), tells him plainly, and offers comfort or a retry.

No version bump: test-agent assets + docs, no production-code change.

agents/README.md

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+# agents/
+
+Persona **source files** for Worldtree Tier 3 (consumer-defined) test
+agents that ratatoskr defines and drives during manual smoke-testing.
+
+These are not pytest fixtures — the automated suite uses mocked wire
+data. They are the authored system-prompt text that gets pushed to the
+live Worldtree server so a real agent exists to observe through the
+ratatoskr TUI / web monitor.
+
+## Files
+
+| File | Agent id | Default model |
+|---|---|---|
+| `sindra.system-prompt.md` | `ratatoskr:sindra` | `artemis-31b-v1i` |
+
+## Source-vs-live: editing a file does not change the agent
+
+A file here is the **script**; the agent on the Worldtree server is the
+**actor**. Editing the file stages new text — the live agent only
+changes when you push it:
+
+```bash
+source ./env.sh                       # WORLDTREE_API_KEY + _API_URL
+python -m ratatoskr.tier3 patch ratatoskr:sindra \
+  --system-prompt "$(cat agents/sindra.system-prompt.md)"
+```
+
+`--system-prompt` takes a literal string, not a path — hence the
+`"$(cat …)"`. Use `define` to create an agent that doesn't exist yet,
+`delete` to hard-remove one. See `python -m ratatoskr.tier3 --help`.
+
+> Prior to this folder these files lived transiently in `/tmp`
+> (`/tmp/personal-worldtree-sindra_system_prompt.md`), which did not
+> survive reboots. The repo copy is now the source of truth; keep it in
+> sync when you `patch` the live agent.