fix(security): audit — fix RUSTSEC vulns, clippy warnings, dead code (#769)

- Upgrade openssl to 0.10.78 (CVE-2026-41676), jsonwebtoken to 9.4
- Suppress unmaintained-only/no-CVE advisories in .cargo/audit.toml
  with per-entry rationale
- Fix all `cargo clippy --all-targets -- -D warnings` errors across
  35 crates: derivable_impls, needless_range_loop, map_or→is_some_and/
  is_none_or, await_holding_lock (drop MutexGuard before .await),
  ptr_arg (&mut Vec→&mut [T]), useless_conversion, approximate_constant
  (2.718→E, 3.14→PI), field_reassign_with_default, manual_inspect,
  useless_vec, lines_filter_map_ok, print_literal, dead_code
- Apply `cargo fmt --all`
- Pre-existing test failure in wifi-densepose-signal
  (test_estimate_occupancy_noise_only) is not introduced by this PR

v2/crates/wifi-densepose-sensing-server/src/cli.rs

@@ -1,7 +1,7 @@
 //! CLI argument definitions and early-exit mode handlers.
 
-use std::path::PathBuf;
 use clap::Parser;
+use std::path::PathBuf;
 
 /// CLI arguments for the sensing server.
 #[derive(Parser, Debug)]