feat(wifi): retry association with backoff in shared connect helper

The single-shot connect_wifi aborted boot on any transient association or
DHCP miss — common right after a reset, when the AP still holds the stale
pre-reset association. Add a bounded retry (5 attempts, 500ms→4s backoff,
disconnect between tries) so those transient failures recover instead of
failing the boot.

Extract the logic into firmware::net (new lib target) and rewire the
wifi_tls / git_push / git_sync spikes to it, removing three duplicated
copies. main.rs reuses this when Wi-Fi lands there instead of adding a
fourth copy.

firmware/src/lib.rs

@@ -0,0 +1,10 @@
+//! Shared library surface for the Typoena firmware crate.
+//!
+//! The editor binary (`src/main.rs`) and the spike binaries under `src/bin/`
+//! are each separate crate roots; anything they need to share lives here and is
+//! reached as `firmware::…`. Currently that is just the resilient Wi-Fi
+//! bring-up, extracted from three duplicated `connect_wifi` copies so the retry
+//! logic lives in exactly one place and the eventual editor integration reuses
+//! it instead of growing a fourth copy.
+
+pub mod net;