Add live Finance Dashboard read model and UI

[theMattCode]

User story

As a user, I want a Finance Dashboard that shows current financial health so I can quickly understand balances, cashflow, budgets, reminders, and investments.

Depends on

• Issue Add balance snapshots and reconciliation calculations #14
• Issue Replace transactions MVP with ledger entries for cashflow and transfers #15
• Issue Add monthly budgets and budget allocation actuals #17
• Issue Add recurring plans and confirmation reminders #18
• Issue Add investment accounts, securities, positions, transactions, and price snapshots #19

Scope

• Add backend API for live dashboard read model computed from finance foundation tables.
• Include net worth and balances grouped by account type.
• Include month-to-date income, expenses, expense reversals, and net cashflow.
• Include current budget progress and over-budget categories.
• Include upcoming reminders requiring action.
• Include investment value, allocation summary, and top positions.
• Add mobile-first Cockpit dashboard route.
• Link each dashboard section to its focused workflow.

Non-scope

• Cached dashboard summary tables.
• External market quote fetching.
• Bank sync/import workflows.

Acceptance criteria

• Dashboard summaries are computed live from finance tables.
• Dashboard separates confirmed actuals from upcoming reminders.
• Net worth subtracts liabilities.
• Transfers do not affect cashflow.
• Budget progress excludes transfers and includes expense reversals.
• Investment values use latest available price snapshots.
• Dashboard is usable on mobile and appealing on desktop.