fix: i18n for remaining hardcoded strings

[BerryUIKI]

Summary

Complete i18n for the remaining hardcoded strings (tasks #4 #7).

Changes

• Locale catalog: added typed zh/en keys (dashboard, performance, agent panel/config, options filters, research dialogs, artifacts)
• TodayPage / OverviewTab / PerformanceTab / ActivityTab: all copy moved to t(), thesis count uses formatMessage
• AgentPanel / AgentConfigGuide: i18n-ized and removed (t as any) fallbacks
• GreeksCalculator / OptionContractTable: i18n-ized (filter tabs, column headers, delete confirmation)
• CreateResearchProjectDialog / CreateAccountDialog: i18n-ized; errors keep err.message
• Tests: dashboard/performance tests wrapped in an en LocaleContext provider

This PR must merge first (the error/artifacts/splits PRs depend on locale keys added here).

[NoviUIKI]

Review summary — PR #140

Verdict: ✅ Approve

Clean, well-typed i18n refactor. I verified the diff, ran the typecheck, and executed the affected tests.

Critical

• None.

Important

• None.

Suggestions (non-blocking)

1. getSampleMessages(t) re-allocates on every render (AgentPanel.tsx:132). The list was previously a module-level constant; each render now rebuilds it. Negligible at 3 items, but worth memoizing if the panel grows.
2. OverviewTab.tsx mixes t with the lower-level translate/formatMessage APIs and a manual !== 1 singular/plural branch. It works for zh/en, but it diverges from the standard t usage elsewhere in this PR and won't generalize to locales with richer plural rules. A small plural helper would keep it uniform.
3. Scope note: the PR also bundles a small behavior change (option-contract delete now surfaces an error banner) and pre-adds artifact-delete keys that a later PR in this stack (#142) actually consumes. Harmless, just slightly beyond "i18n".

Strengths

• Removes the (t("...") as any) || "fallback" pattern in favor of fully typed MessageKey keys. Since MessageKey is the intersection of the zh/en catalogs, a missing key can't even compile.
• Adds htmlFor/id label associations in GreeksCalculator — an accessibility win.
• Wraps the dashboard tests in a LocaleContext.Provider, so they render deterministically (and no longer crash on t).
• CreateResearchProjectDialog validation errors are now localized and the generic failure message is only used when the error carries no message.

Verification

• tsc --noEmit (apps/desktop): passes.
• vitest on PerformanceTab.test.tsx + dashboard-tabs.test.tsx: 12/12 pass.
• git diff --check: clean.