breadlock: fail-secure dispatch errors, zeroize password material, distinguish PAM config errors, fix output leak and key repeat

- main.rs: dispatch-loop errors no longer silently exit; bounded retry with
  loud logging, and explicitly never call unlock() on an error path (would
  turn a fail-secure crash into a fail-open one)
- Cargo.toml/state.rs/keyboard.rs/auth/*: password buffer is now
  Zeroizing<String>, with explicit zero-then-truncate on backspace and
  zeroize on clear/submit; also zeroes pam-client2's internal Conversation
  copy after use
- state.rs/main.rs: new AuthState::ConfigError, distinct on-screen message
  and error!-level log for PAM context-init failures vs ordinary wrong
  password
- lock/surface.rs/state.rs: LockSurface now tracks its wl_output so
  output_destroyed can remove it, fixing the surfaces Vec leak on
  monitor unplug
- input/keyboard.rs: bind the keyboard via get_keyboard_with_repeat so
  held keys (e.g. backspace) actually repeat, regardless of whether the
  compositor implements server-side wl_keyboard repeat

Cargo.lock

@@ -108,6 +108,7 @@ dependencies = [
  "tracing",
  "tracing-subscriber",
  "wayland-client",
+ "zeroize",
 ]
 
 [[package]]
@@ -2247,6 +2248,12 @@ version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6df3dc4292935e51816d896edcd52aa30bc297907c26167fec31e2b0c6a32524"
 
+[[package]]
+name = "zeroize"
+version = "1.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e13c156562582aa81c60cb29407084cdb54c4164760106ab78e6c5b0858cf64e"
+
 [[package]]
 name = "zmij"
 version = "1.0.21"