feat(docs): Add comprehensive documentation for Vexer, Vulnerability Explorer, and Zastava modules

- Introduced AGENTS.md, README.md, TASKS.md, and implementation_plan.md for Vexer, detailing mission, responsibilities, key components, and operational notes.
- Established similar documentation structure for Vulnerability Explorer and Zastava modules, including their respective workflows, integrations, and observability notes.
- Created risk scoring profiles documentation outlining the core workflow, factor model, governance, and deliverables.
- Ensured all modules adhere to the Aggregation-Only Contract and maintain determinism and provenance in outputs.

docs/modules/notify/implementation_plan.md

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+# Implementation plan — Notify
+
+## Delivery phases
+- **Phase 1 – Core rules engine & delivery ledger**  
+  Implement rules/channels schema, event ingestion, rule evaluation, idempotent deliveries, and audit logging.
+- **Phase 2 – Connectors & rendering**  
+  Ship Slack/Teams/Email/Webhook connectors, template rendering, localization, throttling, retries, and secret referencing.
+- **Phase 3 – Console & CLI authoring**  
+  Provide UI/CLI for rule authoring, previews, channel health, delivery browsing, digests, and test sends.
+- **Phase 4 – Governance & observability**  
+  Add approvals, RBAC, tenant quotas, Notify metrics/logs/traces, dashboards, Notify-specific alerts, and Notify runbooks.
+- **Phase 5 – Offline & compliance**  
+  Produce Offline Kit bundles (rules/channels/deploy scripts), signed exports, retention policies, and auditing for regulated environments.
+
+## Work breakdown
+- **Service & worker**
+  - REST API for rules/channels/delivery history, idempotency middleware, digest scheduler.
+  - Worker pipelines for event intake, rule matching, template rendering, delivery execution, retries, and throttling.
+  - Delivery ledger capturing payload metadata, response, retry state, DSSE signatures.
+- **Connectors**
+  - Slack/Teams/Email/Webhook plug-ins with configuration validation, rate limiting, error classification.
+  - Secrets referenced via Authority/Secret store; no plaintext storage.
+- **Console & CLI**
+  - Console module for rules builder, condition editor, preview, test send, delivery insights, digests and schedule configuration.
+  - CLI (`stella notify rule|channel|delivery`) for automation, export/import.
+- **Integrations**
+  - Event sources: Concelier, Excititor, Policy Engine, Vuln Explorer, Export Center, Attestor, Zastava, Scheduler.
+  - Notify events to Notify (meta) for failure escalations, accepted-risk expiration reminders.
+- **Observability & ops**
+  - Metrics: delivery success/failure, retry counts, throttle hits, digest generation, channel health.
+  - Logs/traces with tenant, rule ID, channel, correlation ID; dashboards and alerts.
+  - Runbooks for misconfigured channels, throttling, event backlog, incident digest.
+- **Docs & compliance**
+  - Update Notifications Studio guides, channel runbooks, security/RBAC docs, Offline Kit instructions.
+  - Provide compliance checklist (audit logging, retention, opt-out).
+
+## Acceptance criteria
+- Rules evaluate deterministically per event; deliveries idempotent with audit trail and DSSE signatures.
+- Channel connectors support retries, rate limits, health checks, previews; secrets referenced securely.
+- Console/CLI support rule creation, testing, digests, delivery browsing, and export/import workflows.
+- Observability dashboards track delivery health; alerts fire for sustained failures or backlog; runbooks cover remediation.
+- Offline Kit bundle contains configs, rules, digests, and deployment scripts for air-gapped installs.
+- Notify respects tenancy and RBAC; governance (approvals, change log) enforced for high-impact rules.
+
+## Risks & mitigations
+- **Notification storms:** throttling, digests, dedupe windows, preview/test gating.
+- **Secret compromise:** secret references only, rotation workflows, audit logging.
+- **Connector API changes:** versioned adapter layer, nightly health checks, fallback channels.
+- **Noise vs signal:** simulation previews, metrics, rule scoring, recommended defaults.
+- **Offline parity:** export/import of rules, connectors, and digests with signed manifests.
+
+## Test strategy
+- **Unit:** rule evaluation, template rendering, connector clients, throttling, digests.
+- **Integration:** end-to-end events from core services, multi-channel routing, retries, audit logging.
+- **Performance:** burst throttling, digest creation, large rule sets.
+- **Security:** RBAC tests, tenant isolation, secret reference validation, DSSE signature verification.
+- **Offline:** export/import round-trips, Offline Kit deployment, manual delivery replay.
+
+## Definition of done
+- Notify service, workers, connectors, Console/CLI, observability, and Offline Kit assets shipped with documentation and runbooks.
+- Compliance checklist appended to docs; ./TASKS.md and ../../TASKS.md updated with progress.