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

Cargo.toml

@@ -80,6 +80,12 @@ clap               = { version = "4", features = ["derive", "env"] }
 # ── Build-time ────────────────────────────────────────────────────────────────
 capnpc             = { version = "0.19" }
 
+[workspace.lints.rust]
+unsafe_code = "warn"
+
+[workspace.lints.clippy]
+unwrap_used = "warn"
+
 [profile.release]
 opt-level         = 3
 lto               = "thin"