feat(analytics): add tool usage analysis (#983)

[rodboev]

The tools analytics endpoint already scans tool_calls, but the response only exposes category totals, per-agent category breakdowns, and trend buckets. That makes the analytics page useful for broad shape, but it cannot answer which concrete tools dominate usage under the active filters.

This extends the existing /api/v1/analytics/tools response with a ranked per-tool analysis surface, keeping aggregation in internal/db/analytics.go and preserving the existing category, agent, and trend fields. The Huma route continues to pass the typed response through, the frontend client is regenerated from the updated schema, and the analytics store plus ToolUsage.svelte render the new rows without rebuilding filter logic in the browser.

The scope is intentionally vertical but local to the existing tools analytics path. It does not add a new endpoint or change how tool calls are ingested.

Closes #983

[roborev-ci]

roborev: Combined Review (2582662)

Verdict: No Medium, High, or Critical findings to report.

The only reported issue was Low severity and has been omitted per instructions.

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Reviewers: 2 done | Synthesis: codex, 4s | Total: 5m46s

[roborev-ci]

roborev: Combined Review (17d8feb)

Verdict: No Medium, High, or Critical findings to report.

The only reported issue was Low severity and is omitted per instructions.

---

Reviewers: 2 done | Synthesis: codex, 6s | Total: 3m37s