fix: rebuild modeloptionsgen when codersdk changes (#24543)

`_gen/bin/modeloptionsgen` reflects over `codersdk` struct tags, but
reflection doesn't read source — Go struct tags are compile-time string
literals folded into the type descriptor and emitted into the binary's
`.rodata` section. `reflect.TypeOf(...).Field(i).Tag.Get("enum")` reads
from that baked-in table; the generator cannot consult
`codersdk/chats.go` on disk even if it wanted to.

That means the binary has to be rebuilt whenever those tags change. The
existing Makefile rule only depends on `scripts/modeloptionsgen/*.go`,
and the JSON target lists the binary as an order-only prereq, so `make
gen` happily runs the stale binary after edits to `codersdk/chats.go`
and writes outdated enum values.

Fix: add `$(wildcard codersdk/*.go)` to the binary's prereqs, matching
`clidocgen`. The whole-package wildcard is deliberate — a narrower
prereq would break if someone splits `chats.go`. Cost is negligible:
Go's per-package build cache means unrelated edits recompile one package
and re-link, and the JSON target's own prereqs are unchanged so it
doesn't regenerate.

Makefile

@@ -151,7 +151,7 @@ _gen/bin/metricsdocgen-scanner: $(wildcard scripts/metricsdocgen/scanner/*.go) |
 	@mkdir -p _gen/bin
 	go build -o $@ ./scripts/metricsdocgen/scanner
 
-_gen/bin/modeloptionsgen: $(wildcard scripts/modeloptionsgen/*.go) | _gen
+_gen/bin/modeloptionsgen: $(wildcard scripts/modeloptionsgen/*.go) $(wildcard codersdk/*.go) | _gen
 	@mkdir -p _gen/bin
 	go build -o $@ ./scripts/modeloptionsgen