Remove committed map-generator binary from the repo (#4234)

**Add approved & assigned issue number here:**

N/A — maintainer housekeeping.

## Description:

Removes the committed `map-generator/map-generator` Go binary from the
repo and adds it to `.gitignore`.

The binary is a local build artifact: `npm run gen-maps` runs the
generator with `go run .`, and nothing in the repo (scripts, CI
workflows, docs) references the committed file. Tracking it just causes
opaque binary churn in every PR that touches the generator (e.g. #4227,
#4231). The `.gitignore` entry keeps locally built binaries from being
accidentally re-committed.

## Please complete the following:

- [x] I have added screenshots for all UI updates (no UI changes)
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file (no user-visible text)
- [x] I have added relevant tests to the test directory (no behavior to
test — removes an unused build artifact)

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evanpelle

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

.gitignore

@@ -21,3 +21,6 @@ src/assets/
 *debug*.txt
 eslint_out.txt
 tests/perf/output/
+
+# Locally built Go binary (gen-maps uses `go run .`)
+map-generator/map-generator