feat: track OpenRouter usage (#134)

Store usage information in database to track user behavior (if user is
not BYOK) as a precursor to billing users, e.g.,

Hourly:
```
  {
    _id: ObjectId('69cd2e9a926e4b5665909027'),
    user_id: ObjectId('6975da46d6096ac1b07342c2'),
    hour_bucket: ISODate('2026-04-01T14:00:00.000Z'),
    project_id: '69746440592738ba2708cc34',
    success_cost: 0.014026150000000001,
    failed_cost: 0.024026150312000001,
    updated_at: ISODate('2026-04-01T14:41:37.465Z')
  }
```

Weekly:
```
  {
    _id: ObjectId('69cd2e9a926e4b5665909028'),
    week_bucket: ISODate('2026-03-30T00:00:00.000Z'),
    project_id: '69746440592738ba2708cc34',
    user_id: ObjectId('6975da46d6096ac1b07342c2'),
    success_cost: 0.014026150000000001,
    failed_cost: 0.024026150312000001,
    updated_at: ISODate('2026-04-01T14:41:37.465Z')
  }
```

Lifetime:
```
  {
    _id: ObjectId('69cd2e9a926e4b5665909029'),
    user_id: ObjectId('6975da46d6096ac1b07342c2'),
    project_id: '69746440592738ba2708cc34',
    success_cost: 0.014026150000000001,
    failed_cost: 0.024026150312000001,
    updated_at: ISODate('2026-04-01T14:41:37.465Z')
  }
```

Merge pull request #153 from PaperDebugger/feat/byok

feat: BYOK enhancements

chore: remove hardcoded nodeSelector values from production values

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fix: BYOK (#150)

### Key changes:
- Select models by ID instead of slug so users can have multiple API
keys for the same slug
- Add loading spinner for save/edit actions

fix: add permissions to backend caller workflows (#147)

Co-authored-by: Junyi Hou <junyi@xtras3.tail08d22c.ts.net>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

refactor: deduplicate CI workflows and fix double triggers (#141)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-authored-by: Junyi Hou <junyi@xtras3.tail08d22c.ts.net>

refactor: deduplicate CI workflows and fix double triggers (#140)

Co-authored-by: Junyi Hou <junyi@xtras3.tail08d22c.ts.net>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

feat: add nodeSelector to all deployments (cloudflared→nuc, others→xt…

…ras3)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fix: add permissions to backend caller workflows (#146)

Co-authored-by: Junyi Hou <junyi@xtras3.tail08d22c.ts.net>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>