feat(usage): API key name in Recent Requests + Usage by Combo tracking

[mahdiwafy]

Summary

Adds API key name column to the Recent Requests card and introduces per-combo usage tracking.

Changes

Recent Requests — API Key column

The Recent Requests card now shows which API key was used for each request. Previously only showed: Status | Model | In/Out | When. Now shows: Status | Key | Model | In/Out | When.

Usage by Combo — new table view

• New comboName column in usageHistory table (migration 004)
• comboName flows through the entire request pipeline: chat.js → chatCore → streamingHandler/nonStreamingHandler → requestDetail → saveRequestUsage
• byCombo aggregation in usageDaily and getUsageStats()
• New "Usage by Combo" option in the usage table selector

Files changed (11 files, +108/-20)

File	Change
open-sse/handlers/chatCore.js	Accept comboName param, add to sharedCtx
open-sse/handlers/chatCore/requestDetail.js	Pass comboName to saveRequestUsage
open-sse/handlers/chatCore/streamingHandler.js	Pass comboName to saveUsageStats
open-sse/handlers/chatCore/nonStreamingHandler.js	Pass comboName to saveUsageStats
src/sse/handlers/chat.js	Pass comboName through handleSingleModelChat
src/lib/db/migrations/004-add-combo-name-column.js	New migration — add comboName TEXT column
src/lib/db/migrations/index.js	Register migration 004
src/lib/db/schema.js	Add comboName to schema
src/lib/db/repos/usageRepo.js	comboName in INSERT, SELECT, aggregation, recentRequests
src/shared/components/UsageStats.js	Key column in RecentRequests, Usage by Combo table option

Migration

Migration 004 adds comboName TEXT column to usageHistory. Non-breaking — existing rows get NULL, new rows populate automatically when request comes through a combo.

Testing

• Build: clean
• Sandbox tested with production DB (38K+ rows) — API returns correct keyName and comboName fields in recentRequests
• byApiKey aggregation unaffected (33 entries verified)
• byCombo aggregation works (0 entries for legacy data, will populate for new combo requests)

[Vanszs]

open-sse/handlers/chatCore/sseToJsonHandler.js is skipped. comboName is not destructured in handleForcedSSEToJson and missing from saveUsageStats calls (line 142 & 218).
if sse-to-json fallback triggers (e.g. codex/kimi), combo usage stats will leak/drop (comboName becomes null).

fix sseToJsonHandler.js to pass comboName down, then request re-review.

[mahdiwafy]

Fixed. comboName added to handleForcedSSEToJson params + both saveUsageStats calls in sseToJsonHandler.js. Ready for re-review. @Vanszs