feat: Sprint 1 — production hardening, TLS lifecycle, CI coverage, lint cleanup

- Fix 3 client panics: replace .unwrap()/.expect() with proper error
  handling in rpc.rs (AUTH_CONTEXT lock), repl.rs (pending_member),
  and retry.rs (last_err)
- Add --danger-accept-invalid-certs flag with InsecureServerCertVerifier
  for development TLS bypass, plus mdBook TLS documentation
- Add CI coverage job (cargo-tarpaulin) and Docker build validation
  to GitHub Actions workflow, plus README CI badge
- Add [workspace.lints] config, fix 46 clippy warnings across 8 crates,
  zero warnings on all buildable crates
- Update Dockerfile for all 11 workspace members

crates/quicproquo-p2p/Cargo.toml

@@ -5,6 +5,9 @@ edition     = "2021"
 description = "P2P transport layer for quicproquo using iroh."
 license     = "MIT"
 
+[lints]
+workspace = true
+
 [dependencies]
 iroh        = "0.96"
 tokio       = { version = "1", features = ["macros", "rt-multi-thread", "time", "sync"] }