feat(curator): deploy the phase-0 system prompt, and correct a misleading README figure

The workspace now holds .pi/SYSTEM.md and .pi/APPEND_SYSTEM.md and nothing else.

SYSTEM.md is rewritten for what is actually deployed. The version committed in
07dd648 described five tools that will not exist until phase 3; shipping it would
have invited the model to call tools it does not have. The capability section now
states plainly that the agent has no tools and that every fact arrives in the
request. The phase-3 target, including the full tool-bearing launch contract, is
recorded in the plan as §4b together with why each part cannot be enabled sooner.

profile.toml likewise describes the deployed configuration rather than the target,
so that deploy-scenario.sh validates against reality and the path check means
something.

Recovered from the retired SKILL.md and folded into SYSTEM.md: the rule that the
current request's schema and length limits override everything else, and that a
JSON task returns exactly one JSON value with no fences. Phase 0's four prompt
types all depend on it, and it was the one part of that file not already covered.

Measured before and after on the real workspace, with flags read from the code
rather than transcribed (docs/evidence/2026-08-27-curator-phase0-prompt.md):

- expert coding assistant framing: present -> gone
- pointer to pi's own documentation: present -> gone
- the 64-line media policy: absent -> present
- workspace AGENTS.md: loaded -> blocked
- parent-directory AGENTS.md: LEAKED -> blocked
- <available_skills>: absent both times

Two things this confirms on the production configuration rather than a synthetic
probe. --skill was genuinely a no-op: it pointed at a real 64-line SKILL.md and
the skills block was still absent, because pi emits it only when a tool named
read is active and --no-tools deactivates everything. And --no-context-files is
the only switch that stops parent-directory pollution: a marker planted in
/home/claw/pi-workspaces/AGENTS.md reached the prompt before and not after.

Deleting the now-dead AGENTS.md and SKILL.md from the workspace changed the
prompt length by zero bytes, which is the proof that they were dead.

README corrected. Its table cited 960 characters as Curator's system prompt after
the change; that figure came from a few-line stub SYSTEM.md in the isolation
probe, and the real prompt is 3539 -- larger, not smaller. Presenting the stub
measurement as Curator's was misleading, and "72% smaller" was wrong. The prompt
grew because roughly 1.9 KB of pi scaffolding was replaced by domain policy that
had never loaded at all. The mechanism claim is unaffected.

README.md

@@ -39,18 +39,32 @@ active** (`dist/core/system-prompt.js:59,113`). The Curator service ran with
 - and both the README and the deployment runbook described a mechanism that was
   not happening.
 
-Measured effect of fixing the flags and adding `.pi/SYSTEM.md`:
+Measured on the real workspace, before and after
+([evidence](docs/evidence/2026-08-27-curator-phase0-prompt.md)):
 
-| Configuration | system prompt | active tools | skills visible | coding-assistant persona |
-|---|---:|---|---|---|
-| `--no-tools` (as found) | 1859 | none | **no** | yes |
-| no isolation flags | 3413 | own + `read` | 3 foreign | yes |
-| `+ --no-skills --skill` | 2619 | own + `read` | 1, correct | yes |
-| `+ .pi/SYSTEM.md --approve` | **960** | own + `read` | 1, correct | **no** |
+| | before | after |
+|---|---|---|
+| system prompt | 2548 chars | 3539 chars |
+| `expert coding assistant` framing | present | **gone** |
+| pointer to pi's own documentation | present | **gone** |
+| the 64-line media policy | **absent** | present |
+| `<available_skills>` | absent | absent |
+| workspace `AGENTS.md` | loaded | blocked |
+| parent-directory `AGENTS.md` | **leaked** | blocked |
 
-72 % smaller *and* strictly more capable. Reproduce with
-[`docs/evidence/probe-harness/`](docs/evidence/probe-harness/) — it costs zero
-model tokens, because a single RPC `get_state` starts the agent, fires
+The prompt got *larger*, and that is the fix rather than its cost: of the
+original 2548 characters roughly 1.9 KB was pi's coding-assistant scaffolding and
+a pointer telling the agent to read pi's documentation and follow its
+cross-references — noise for a media agent, and a ready-made escalation path for
+injected text — while none of it was Curator's own policy. All 3539 characters
+now are.
+
+A mechanism demonstration with a stub `SYSTEM.md` is in
+[`docs/evidence/2026-08-27-isolation-probe.md`](docs/evidence/2026-08-27-isolation-probe.md);
+its 960-character figure measures the stub, not Curator.
+
+Reproduce either with [`docs/evidence/probe-harness/`](docs/evidence/probe-harness/)
+— zero model tokens, because a single RPC `get_state` starts the agent, fires
 `session_start` and exits without contacting the provider.
 
 ## Layout