docs: align SDD / REQUIREMENTS / SPEC v0.0.3 with closed open issues

ARCHITECTURE.md -> 0.0.3
REQUIREMENTS.md -> 0.0.2
SPEC.md         -> 0.0.2

Closed OI-01 through OI-06 with concrete decisions:
- OI-01: Encryption at rest delegated to hardware-host (no OS-level LUKS,
  no column-level). Compliance intent preserved at infrastructure layer.
- OI-02: Argon2id starting parameters m=64MiB, t=3, p=1; 250-500 ms
  login-latency budget on Intel Xeon 4c/16GB; calibration recorded in
  system_config at deploy time.
- OI-03: JWT signing = EdDSA/Ed25519; 90-day key rotation with 24-hour
  overlap; web holds signing key, worker holds verifying key only.
- OI-04: CIDR scan concurrency = 128, per-host timeout = 1.5 s; /22 across
  sites completes under 10 s; progress UI + cancel required.
- OI-05: PDF stack = printpdf + plotters (in-process, no sidecar);
  charts required; no branding; no digital signatures.
- OI-06: /status/health = minimal unauthenticated liveness;
  /api/v1/status/fleet = authenticated fleet aggregates.

Added architecture decisions:
- AD-15: Web UI TLS certificate strategy (self-signed from internal CA
  by default; operator may supply external cert)
- AD-16: Azure SSO + SMTP runtime configuration via Settings GUI with
  test-connection actions
- AD-17: PDF generation via printpdf + plotters
- AD-18: IP whitelist enforcement at every listener

Added FR-07 (System Configuration) in REQUIREMENTS.md covering Azure
SSO GUI, SMTP GUI, polling-interval tuning, Web UI TLS strategy,
and IP whitelist management.

SDD review pass also added (from v0.0.2):
- IEEE 1016-aligned structure (Introduction, Stakeholders, Design
  Rationale, Risks, Open Issues, Glossary, References, Revision History)
- Portable ASCII diagrams; split into Context/Logical/Deployment/Process
  views
- Explicit WebSocket ticket authentication flow
- Rollback data flow (6.5)
- API error envelope + X-Request-Id correlation
- Configuration, migration, and backup/DR sections
- Worker heartbeat and dead-process detection
- Sizing math for 2,500-host scalability claim
- Split /status/health (Manager) from /api/v1/health (Agent) namespaces

See ARCHITECTURE.md section 18 for the full change log.

.gitignore

@@ -12,3 +12,7 @@ venv/**
 # IDE
 .vscode/
 .idea/
+
+# Backup files
+*.bak
+*.bak.*