docs: resolve OQ-04, remove OQ-07, enrich OQ-03 with rolling windows

- OQ-04 resolved: thresholds are both model-specific (shipped with
  codebook) and user-overridable. Inspired by platonic representation
  hypothesis — calibrated models converge on similar behavioral patterns.
- OQ-07 removed: Rust port is an alknet project concern, not relevant
  to the Python package architecture. Removed from overview.md Phase 3.
- OQ-03 enriched: rolling window token screening for granular detection
  in documents (PDF→markdown use case, academic paper injection detection).
  Upgraded from low to medium priority.
- OQ-01 updated: likely path is PyTorch first, ONNX export by default.
- OQ-05 updated: needs deep dive into guardrail landscape.
- Updated threshold description in configuration.md with platonic
  representation context.

docs/architecture/firewall.md

@@ -196,5 +196,5 @@ All exception types subclass `AlknetFirewallError` (base library exception).
 Open questions are tracked in [open-questions.md](open-questions.md). Key
 questions affecting this document:
 
-- **OQ-03**: Should the firewall support streaming/chunked input screening? (open)
-- **OQ-05**: How should the firewall integrate with existing guardrail systems? (open)
+- **OQ-03**: Should the firewall support streaming/chunked input screening? (open — rolling window approach is promising)
+- **OQ-05**: How should the firewall integrate with existing guardrail systems? (open — needs research)