feat(WP-0003c): context adapters, first ActivityDefinition, full test suite

T51: ContextResolver ABC + CONTEXT_RESOLVER_REGISTRY; resolve_context activity
updated to dispatch via registry (warns + binds {} on failure, never aborts run).
T52: RepoScopingContextResolver with 5-min in-process cache.
T53: StateHubContextResolver (no cache) for domain_summary and repo_sbom_status.
T54: activity-definitions/weekly-sbom-staleness.md (Monday 09:00 Berlin, cron
trigger, flag-stale-sbom rule at >30 days) + tasks/sbom-rescan.md template.
T55: 51 parametrized evaluator tests — all whitelisted operators, unsafe
expression rejection, empty condition, missing attribute, nested context access.
T56: 15 executor safety tests — UntrustedFieldError, object-type rejection,
injection fixture, LLM retry on bad JSON, review_required field.
T57: 6 integration tests — parses real definition, evaluates rule per-repo
(stale/fresh boundary), emits via NullSink, verifies spawn log entries.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

activity-definitions/weekly-sbom-staleness.md

@@ -0,0 +1,34 @@
+---
+id: weekly-sbom-staleness
+name: Weekly SBOM Staleness Check
+enabled: true
+owner: custodian-agent
+governance: custodian
+status: active
+trigger:
+  type: cron
+  cron_expression: "0 9 * * 1"
+  timezone: Europe/Berlin
+  misfire_policy: skip
+context_sources:
+  - type: state-hub
+    query: repo_sbom_status
+    params:
+      repos: all
+    bind_to: context.repos
+---
+
+# Weekly SBOM Staleness Check
+
+Runs every Monday at 09:00 Berlin time. Checks all tracked repositories for
+SBOM staleness and flags any repository whose SBOM is older than 30 days.
+
+```rule
+id: flag-stale-sbom
+condition: 'context.repos.sbom_age_days > 30'
+action:
+  task_template: tasks/sbom-rescan.md
+  target_repo: context.repos.repo_slug
+  priority: medium
+  labels: ["sbom", "security", "automated"]
+```