feat: implement the open fallback access point and captive portal

PLANS.md

@@ -2263,7 +2263,7 @@ When all criteria pass, set this milestone to `DONE` and change Milestone 006 to
 
 ## Milestone 028 — Implement the open fallback access point and captive portal
 
-**Status:** `BLOCKED`  
+**Status:** `DONE`
 **Depends on:** Milestone 027
 
 ### Objective
@@ -2294,6 +2294,14 @@ Give users access to the game and external-network configuration through the ope
 
 When all criteria pass, set this milestone to `DONE` and change Milestone 007 to `READY`.
 
+### Execution record
+
+- Date: 2026-09-01
+- Result: PASS.
+- Evidence: The user completed the required physical fallback-network checks with no issues: discovery and open connection to `Battleship-open`, captive-portal redirection and direct setup-page access, responsive scanning/manual hidden-SSID entry, game HTTP/WebSocket access for players and spectators, bounded invalid-input handling, and no credential disclosure.
+- Verification: Host captive-portal and network-foundation tests, browser tests/syntax checks, firmware build, and LittleFS build passed during implementation.
+- Next action: Milestone 029 remains blocked and was not started.
+
 ---
 
 ## Milestone 029 — Validate credentials, persist them, and switch without rebooting