docs: reorganize api docs into categorized subdirectories and fill missing docs
- Categorize 77 existing api docs into 16 business-domain subdirectories
(auth/ad/wallet/coupon/compare/savings/signin/tasks/invite/user/
device/platform/intent/meituan/other) plus admin/ and internal/
- Split admin/ into 7 sub-resource subdirectories (auth/users/wallet/
withdraws/feedbacks/admins/ad) with 4 single-file docs at root
- Create 21 new docs covering 28 previously undocumented endpoints:
ad/watch-report, wallet/transfer-auth (3 endpoints), coupon/session+
stats+completed-today+prompt (7), invite/me+invitees+bind+landing-track,
user/onboarding (2), platform/flags+ad-config+app-version,
intent/step+precoupon/step, analytics/events, order/report,
report/submit+records, feedback/config+records, trace/finalize
- Add mock request/response JSON examples to all new docs
- Create docs/README.md with full category index for LLM navigation
- Update docs/api/README.md: fix all links, add new endpoint rows,
replace "no doc" markers with actual links
- Fix back-navigation links (./README.md -> ../README.md or
../../README.md) in all moved files
@
guke