* feat(api): structured ?format=json for the self-service usage endpoint
GET /api/usage/om-usage already let any key read its own usage — personal
daily/weekly USD limits and the provider quota snapshot — but only as
text/plain, which a UI cannot parse safely. OmniCopilot issue #8 asks exactly
for this surface.
Adds ?format=json, returning the ApiKeyUsageLimitStatus + UsageSnapshot the
text is rendered from. Text and JSON share the same collectors
(collectUsageSnapshots, getApiKeyUsageLimitStatus), so the two can never
disagree about a number. The response is a discriminated union: a key without
allowUsageCommand (403) or an invalid key (401) returns
{ allowed:false, error:{message} }, distinct from allowed:true with empty
sections — the state a panel must render as "nothing learned yet", not a
refusal. Text form unchanged; without ?format the contract is untouched.
The endpoint was previously missing from API_REFERENCE.md; it now has a
section documenting both forms, the allowUsageCommand gate, and the
self-service auth model (caller's own key, not requireManagementAuth).
Regression guards in tests/unit/usage-command-json-format.test.ts (4 tests:
json shape, text default preserved, structured 403, sanitized 401 with no
stack trace). Existing internal-usage-command suite still 12/12.
* chore(changelog): correct the fragment to the real PR number (#11190)
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Co-authored-by: Xiangzhe <bakryun0718@proton.me>
