refactor: consolidate types, remove dead code, and fix minor bugs

Replace DayOfWeek with chrono::Weekday via extension traits, unify
RateLimitConfig into the config module, and remove the unused time
command, BannerState, and ClassDetails stub. Fix open_only query
parameter to respect false values and correct 12-hour time display.

Cargo.lock

@@ -230,6 +230,7 @@ dependencies = [
  "cookie",
  "dashmap 6.1.0",
  "dotenvy",
+ "extension-traits",
  "figment",
  "fundu",
  "futures",
@@ -806,6 +807,35 @@ dependencies = [
  "pin-project-lite",
 ]
 
+[[package]]
+name = "ext-trait"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b0c24fe28375ffabb5479233d60a5d99930a3983ed3aa6db66dd03b830fc41b2"
+dependencies = [
+ "ext-trait-proc_macros",
+]
+
+[[package]]
+name = "ext-trait-proc_macros"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ad551ddce9af58215158c84e1e655b2011f6355b655c13b56d88986b14d3db98"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.106",
+]
+
+[[package]]
+name = "extension-traits"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e5fea67d50388b3db0e51e65815ed7293703607ff9dc50d86f93e1abcc67b572"
+dependencies = [
+ "ext-trait",
+]
+
 [[package]]
 name = "fastrand"
 version = "2.3.0"