docs: update ARCHITECTURE.md and README for 1.0.x fixes

ARCHITECTURE.md:
- Cookie secure flag: NODE_ENV → TRUST_PROXY (3 locations)
- upgrade-insecure-requests: document it gates on TRUST_PROXY not NODE_ENV
- Docker image note: NODE_ENV=production no longer implies secure cookies
- Security checklist: clarify TRUST_PROXY enables secure cookie + CSP + HSTS
- dashboard.js route table: add /stream endpoint note
- NODE_ENV env var table: correct description

README.md:
- qBittorrent availability: note red highlight when < 100%
- Login side-effects: secure cookie gated on TRUST_PROXY not NODE_ENV

README.md

@@ -263,7 +263,7 @@ sofarr polls all configured services in the background and caches the results. D
 ### For qBittorrent Downloads
 - **Seeds** - Number of seeders
 - **Peers** - Number of peers
-- **Availability** - Percentage available in swarm
+- **Availability** - Percentage available in swarm (shown in red when below 100%)
 
 ## API Endpoints