docs+tests: architecture diagram, security docs, 75 new edge-case tests
README:
- Add ASCII architecture flow diagram showing all layers
- Add Security Architecture section (Layer 1: Channel Auth,
Layer 2: Rate Limiting, Layer 3: Tool Sandbox)
- Update test count to 629
New edge-case tests (75 new):
- SecurityPolicy: command injection (semicolon, backtick, dollar-paren,
env prefix, newline), path traversal (encoded dots, double-dot in
filename, null byte, symlink, tilde-ssh, /var/run), rate limiter
boundaries (exactly-at, zero, high), autonomy+command combos,
from_config fresh tracker
- Discord: exact match not substring, empty user ID, wildcard+specific,
case sensitivity, base64 edge cases
- Slack: exact match, empty user ID, case sensitivity, wildcard combo
- Telegram: exact match, empty string, case sensitivity, wildcard combo
- Gateway: first-match-wins, empty value, colon in value, different
headers, empty request, newline-only request
- Config schema: backward compat (Discord/Slack without allowed_users),
TOML roundtrip, webhook secret presence/absence
629 tests passing, 0 clippy warnings
a5887ad2dc