Implement mecatui tool-call inspector

[jbeda]

Implementation

Implements the keyboard-first, current-session /toolcalls inspector approved in the Plan / Interface PR #2056, merged at 9edd9b751f22c4deb5f5d0b03308e77ff06ba5d2.

• AC1.1–1.3: local command, chronological top-level call inventory, stable live navigation and resumed-session scope.
• AC2.1–2.3: live call detail, long-content scrolling and follow, typed/structured MCP results and honest binary descriptions.
• AC3.1–3.3: full-region/compact layout, modal input and session lifecycle isolation, updated TUI usage and contributor guidance.
• AC4.1–4.3: readable one-line intents, complete labeled arguments and nested-field fallback, scan-friendly detail sections and inspector-only Read result gutter spacing.
• AC5.1–5.2: primary click selects a visible inspector row by stable block identity; Enter still opens detail. Stale/hidden hits and no-mouse configurations do not select.
• Review polish: list uses bounded above/below indicators and full-region fill like other browsers; detail uses tool-theme tones and distinct indented argument keys/values while keeping long results flush-left. Wheel scrolling changes the list window without moving selection; scrolling back to the tail restores live follow. List and detail carry the tool-card …/✓/✗ status glyphs, semantic colors, and non-color text labels. Contributor status and wheel conventions live in docs/tui.md.

Content-type-specific result rendering (diff colors, Markdown, Shell, JSON) and a dedicated rendering boundary are tracked in follow-up #2066, not implemented here.

Interfaces match approved contract: Yes, with the directing operator's in-PR amendment. Plan amendment 4b7de7d89 explicitly authorizes the presentation and inspector-row click scope following hands-on review. No other implementation deviation required an amendment. Existing conversation cards and global ctrl+t behavior are unchanged; conversation-card clicking and quieter cards remain separate work under #1361.

Verification

• task docs, task site:build, task ac-trace-strict (14 ACs, 0 failures): passed.
• task test, task lint, GOFLAGS=-p=2 task test:race: passed on the final source and tests. An unconstrained race attempt hit an unrelated intermittent server assertion and an internal/app test timeout; the isolated server test and full suite with reduced package concurrency passed.
• Offline go run ./cmd/mecademo: tool call, permission ask/approval, and tool result observed.
• Four-axis panel and repair revalidation: PANEL: ship_blockers=0 important=0 advisory=0 reviewer_failures=0.

Relates to #1361