feat(viewer): show result type and length in the status line

[laurigates]

Summary

After each query, the status line now reports the type and length of the current result, so you don't have to append | type / | length to inspect a result's shape (#72).

Examples:

• result: object · 3 keys
• result: array · 5 items
• result: string · 12 chars
• result: number / boolean / null
• result: stream · N values (multi-value output)
• result: empty (0 results)

Implementation

• A pure json::summarize(&[Value]) -> String helper mirrors jq's type/length semantics; it's unit tested (objects/arrays/strings, scalars, streams, empty, and Unicode char counting).
• Surfaced through the existing guide/status mechanism (GuideMessage::ResultSummary) on the query-success path — no layout changes. Null and error results keep their existing messages.

Scope note

This shows the summary in the existing status line, which updates on each query result (the moment the shape matters). The issue mentions a vim-style persistent corner/bottom line; that would need a new dedicated render slot and layout rework. Happy to follow up with a persistent statusline if you'd prefer that direction — kept this change minimal and self-contained.

Closes #72

[laurigates]

Related PRs (no strict merge order) — #120, #121, and #122 are a small series of viewer / status-line improvements that independently edit the same code (refresh_view_with_query in src/json_viewer.rs, and src/guide.rs). They're independent in intent but overlap textually, so whichever merges first, the others will need a quick rebase — no specific order is required.