Expose skill usage in analytics so the dashboard and insights output can
show which skills the agent loads and manages over time.

This adds skill aggregation to the InsightsEngine by extracting
`skill_view` and `skill_manage` calls from assistant tool_calls,
computing per-skill totals, and including the results in both terminal
and gateway insights formatting. It also extends the dashboard analytics
API and Analytics page to render a Top Skills table.

Terminology is aligned with the skills docs:
  - Agent Loaded = `skill_view` events
  - Agent Managed = `skill_manage` actions

Architecture:
  - agent/insights.py collects and aggregates per-skill usage
  - hermes_cli/web_server.py exposes `skills` on `/api/analytics/usage`
  - web/src/lib/api.ts adds analytics skill response types
  - web/src/pages/AnalyticsPage.tsx renders the Top Skills table
  - web/src/i18n/{en,zh}.ts updates user-facing labels

Tests:
  - tests/agent/test_insights.py covers skill aggregation and formatting
  - tests/hermes_cli/test_web_server.py covers analytics API contract
    including the `skills` payload
  - verified with `cd web && npm run build`

Files changed:
  - agent/insights.py
  - hermes_cli/web_server.py
  - tests/agent/test_insights.py
  - tests/hermes_cli/test_web_server.py
  - web/src/i18n/en.ts
  - web/src/i18n/types.ts
  - web/src/i18n/zh.ts
  - web/src/lib/api.ts
  - web/src/pages/AnalyticsPage.tsx