feat(headroom): make the compression request timeout configurable

The 3000 ms timeout on /v1/compress was fixed, so busy or slow machines
timed out often and sent the LLM an inconsistently compressed body,
hurting prompt caching. Add a headroomTimeoutMs setting, thread it from
the chat handler down to compressWithHeadroom, expose it in the Token
Saver dashboard, and normalize invalid values back to the 3000 ms default.

src/lib/db/repos/settingsRepo.js

@@ -53,6 +53,7 @@ const DEFAULT_SETTINGS = {
   headroomEnabled: false,
   headroomUrl: DEFAULT_HEADROOM_URL,
   headroomCompressUserMessages: false,
+  headroomTimeoutMs: 3000,
   cavemanEnabled: false,
   cavemanLevel: "full",
   ponytailEnabled: false,