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/Cargo.toml

@@ -10,6 +10,13 @@ rust-version = "1.85"
 # rust-analyzer — see README "harness = false" note).
 autobins = false
 
+# Shared library surface (currently just resilient Wi-Fi bring-up in
+# `firmware::net`), reused by the editor bin and the spike bins so the connect
+# retry logic lives in exactly one place rather than being copied per binary.
+[lib]
+name = "firmware"
+path = "src/lib.rs"
+
 [[bin]]
 name = "firmware"
 path = "src/main.rs"