fix: nil-close bug, stale docs, dead code, and tracked binaries

- Fix potential nil file.Close() panic in devModePersist/devModeRemovePersisted
  by extracting loadDevModeMap/saveDevModeMap helpers with proper defer
- Remove tracked binaries (pathparams 10.8 MB, shake.db 22 MB) and consolidate
  .gitignore with a wildcard pattern covering all 19 examples
- Remove stale reaper reference in README (removed in dc56261), update example
  count from 14 to 19, fix OnChange debounce claim in docs
- Fix typos: "percist"→"persist", "percisted"→"persisted", "tmplates"→"templates"
- Remove dead code: commented import in signal_test.go, unnecessary fmt.Sprintf
  in computed.go, commented picocss imports and no-op Config calls in examples
- Replace go fmt with gofmt -l check in ci-check.sh to fail on unformatted code
  instead of silently reformatting

.gitignore

@@ -37,18 +37,9 @@ go.work.sum
 # Air artifacts
 *tmp/
 
-# binaries
-internal/examples/chatroom/chatroom
-internal/examples/counter/counter
-internal/examples/countercomp/countercomp
-internal/examples/greeter/greeter
-internal/examples/livereload/livereload
-internal/examples/picocss/picocss
-internal/examples/plugins/plugins
-internal/examples/realtimechart/realtimechart
-internal/examples/shakespeare/shakespeare
-internal/examples/nats-chatroom/nats-chatroom
-/nats-chatroom
+# Example binaries and data files
+internal/examples/*/[a-z]*[!.go]
+internal/examples/shakespeare/shake.db
 
 # NATS data directory
 data/