#15650: fix(whatsapp): pass fileName to document sends instead of hardcoding 'file'

#### Summary Fix WhatsApp outbound documents always showing as "file" — the fileName from `loadWebMedia()` is now passed through to the Baileys `sendMessage` handler. Fixes #15560 #### Behavior Changes - Documents sent via WhatsApp now display their actual filename (e.g., `report.pdf`) instead of generic `file` - No breaking changes — falls back to `"file"` if fileName is undefined #### Codebase and GitHub Search - Searched for existing fileName handling: found `loadWebMedia()` already returns `fileName` but it was not passed through - Verified no other code paths affected #### Tests - Updated `src/web/outbound.test.ts` to expect the new sendOptions with fileName - `pnpm test -- --run src/web/outbound.test.ts` passes (9/9) - `pnpm build` passes #### Manual Testing (omit if N/A) Not tested on live WhatsApp — requires paired device. Fix is straightforward pass-through. lobster-biscuit **Sign-Off** - Models used: Claude Opus 4.5 - Submitter effort (self-reported): AI-assisted, human-reviewed - Agent notes: Code change is minimal (3 files, ~10 lines). The fix adds `fileName?: string` to `ActiveWebSendOptions`, captures `media.fileName` in `outbound.ts`, and uses `sendOptions?.fileName || "file"` in `send-api.ts`. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR threads the `fileName` returned by `loadWebMedia()` through WhatsApp outbound sending so Baileys document messages use the real filename instead of a hardcoded `"file"`. Concretely, it adds `fileName?: string` to `ActiveWebSendOptions`, captures `media.fileName` in `src/web/outbound.ts`, and uses `sendOptions?.fileName || "file"` when constructing the Baileys document payload in `src/web/inbound/send-api.ts`. Tests were updated to assert the new send options object. <h3>Confidence Score: 4/5</h3> - This PR is likely safe to merge after addressing one small behavioral consistency issue in outbound sendOptions construction. - Changes are narrowly scoped and covered by a unit test, but `sendOptions` now sometimes includes `accountId: undefined` when the options object exists solely to pass `fileName`, which can be behaviorally different from omitting the field if downstream logic checks for property presence rather than value. - src/web/outbound.ts _{Last reviewed commit: 7740fbd} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->