feat(posture): add deterministic feedback proposals

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a02929-244b-7391-b933-c04010e8eedb

examples/posture-feedback/README.md

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+# Posture Feedback Example
+
+`expired-e2.yaml` is deliberately valid as a posture declaration while carrying
+expired E2 evidence at the example evaluation time. It also has posture and
+zone reviews due within 14 days, an E3 control awaiting evidence, and one
+declared retention gap.
+
+The evaluator reports these as proposals and performs no mutation:
+
+```bash
+uv run tools/posture-feedback/posture_feedback.py \
+  --as-of 2026-08-23T12:00:00Z \
+  --horizon-days 14 \
+  --fail-on none \
+  examples/posture-feedback/expired-e2.yaml
+```

examples/posture-feedback/expired-e2.yaml

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+schema_version: "0.1"
+framework: netkingdom-tenancy-posture
+service: example-security-api
+role: tenant-api
+responsible_repo: net-kingdom
+
+workload_identity:
+  name: example-security-api
+  kind: application
+  responsible_repo: net-kingdom
+  identity_bindings:
+    - scheme: iam-profile
+      authority: key-cape
+      subject: example-security-api
+      principal_type: service
+      environment: reference
+
+tenancy:
+  current: {I: 1, A: 2, E: 2, P: 0, R: 1, V: 0}
+  implemented: {E: 3}
+  target: {I: 2, A: 3, E: 3, P: 1, R: 2, V: 1}
+  reviewed: "2026-08-01"
+  review_due: "2026-08-31"
+  service_class: interactive
+  reason:
+    I: Request identity is not verified in this reference fixture.
+    P: Reference fixture has no provisioned datastore.
+    R: Platform default retention applies.
+    V: No availability exercise exists.
+  gap:
+    R: Publish and evidence an explicit erasure horizon.
+
+zones:
+  standard: security-zones_v0.1
+  membership: z1-operational
+  responsible_party: team:platform-security
+  justification: Reference workload with bounded internal data.
+  context:
+    maturity: M1
+    criticality: medium
+    data_classification: internal
+  evidence:
+    - ref: docs/evidence/reference-zone.md
+      supports: [M1, reference]
+  reviewed: "2026-08-01"
+  review_due: "2026-08-25"
+
+evidence:
+  A2: docs/evidence/reference-authorization.md
+  E2: docs/evidence/reference-adversarial-e2.md
+
+evidence_freshness:
+  E2:
+    kind: adversarial
+    observed_at: "2026-08-20T12:00:00Z"
+    valid_until: "2026-08-22T12:00:00Z"
+    responsible_repo: net-kingdom
+    scope: Two bounded cross-tenant read probes against the reference fixture.
+    remediation: Repeat the bounded E2 probes and replace the evidence metadata.
+    source_revision: reference@0000000