fix(api/dashboard): tighten committed_monthly aggregation (status + unit + account scope)

[cristim]

Summary

Three bugs were inflating the committed_monthly KPI on the Home page:

1. Status filter: isActiveCommitment now rejects rows whose Status field is non-empty and not "completed". DB-backed purchase_history rows always read back with Status="" (the column is not persisted — dynamodbav:"-"). Synthesised rows from failed/cancelled/expired executions carry a non-empty status and were being counted as active commitments.

2. Unit verification: Confirmed and documented that EstimatedSavings is always written in monthly units (populated from PurchaseExecution.EstimatedSavings which derives from monthly recommendation savings at purchase time). No runtime normalisation is needed; comment added to prevent future drift.

3. Multi-account scope: resolveDashboardAccountID was passing "" to GetPurchaseHistory when account_ids had multiple entries, yielding WHERE account_id = '' which returns no rows at all (silently zero, not all-accounts). Replaced resolveDashboardAccountID with resolveDashboardAccountScope that:

   • Routes to GetPurchaseHistoryFiltered(cloudAccountUUIDs) (matches cloud_account_id = ANY($1)) for UUID-based account_ids filters
   • Routes to GetPurchaseHistory(legacyAccountID) for the legacy singular account_id param
   • Routes to GetAllPurchaseHistory when no filter is set
   • Also fixes the single-UUID case, which was passing a UUID to the VARCHAR account_id column

New test assertions

• status=failed row is excluded from committedMonthly and activeCommitments
• Multi-account UUID filter routes to GetPurchaseHistoryFiltered (not GetPurchaseHistory), and the mock asserts GetPurchaseHistory is never called
• No-filter path uses GetAllPurchaseHistory (updated 5 existing tests to match the new dispatch)

Test plan

• go test github.com/LeanerCloud/CUDly/internal/api/... -run TestHandler_calculateCommitmentMetrics passes (8 tests including 3 new)
• go test github.com/LeanerCloud/CUDly/internal/api/... passes (all 1387 tests)
• go test ./... passes (5016 tests)
• Home page KPI shows expected value with a few commitments, not inflated total

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: e929decc-2601-452c-ba54-c0d16ac21bc3

📥 Commits

Reviewing files that changed from the base of the PR and between 1dbeef7 and 16e1e18.

📒 Files selected for processing (4)

• internal/api/handler_dashboard.go
• internal/api/handler_dashboard_test.go
• internal/api/handler_per_account_perms_test.go
• internal/api/handler_test.go

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/committed-monthly

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