feat: Rust port of the data/UI half (export, push, scan, inspect)

[dacorvo]

What

Phase 1 of porting agentcap from Python to a single static Rust binary: the data/UI half — export, HF push, the trufflehog scan gate, ls, and the inspect terminal UI. It builds alongside the existing Python package (src/agentcap/), which stays working and is removed per-command as each reaches parity.

The capture/runtime half (run, the HTTP capture proxy, podman sandbox, agent drivers, orchestrator) is out of scope here — a separate later phase. Until then the Python run produces the captures this half consumes; the on-disk .agentcap/ layout is the contract between the two.

Modules

• export — render each capture dir to parquet (exact 13-column schema, with agent/model/tasks in the key-value metadata), then push paired <owner>/<base>-captures + per-agent <owner>/<base>-<agent>-traces datasets and group them in a Collection. One commit per push.
• scan — trufflehog over captures/ traces/ sessions/: verified hits abort, unverified are surfaced but non-blocking; results cached to scan.json; --no-scan to skip.
• inspect — in-process ratatui + nucleo picker chain (run → request → message, plus local-parquet and hf:// flows) replacing the whole fzf/--listen/preview-subprocess pipeline. Live fuzzy filter, message-diff preview with query highlighting, Esc walk-back. The HF flow streams a footer-read picker (ranged reads, no full download) that fills in as metadata arrives.
• ls — workspace run listing.

Design notes

• Synchronous throughout — uses hf-hub's blocking API (each op wraps its own runtime), so there's no tokio to manage; inspect's footer concurrency uses std threads + an mpsc channel feeding the UI.
• hf-hub only for the Hub (auth, ranged footer reads, commits); Collections go through a small reqwest::blocking REST call (no hf-hub Collections API).
• Captures live in HF Dataset repos (hf://datasets/owner/name).
• inspect parses each parquet once into an in-memory map and caches the preview, so navigation stays instant even on large files.

Verification

• cargo fmt --check, cargo clippy --all-targets -- -D warnings, and cargo test (52 tests) all green. The pure helpers (SSE decode, message diff, fzf-term parsing, rid resolution, parquet round-trip) are ported with their Python tests.
• Cross-impl: pyarrow reads a Rust-written parquet — schema/column-order, agent/model/tasks KV, non-ASCII content, and the streamed-response wrapper all match the Python exporter's output, so existing Python consumers load Rust-produced datasets unchanged.
• Manual: ls, the three inspect flows, and a live export --push round-trip exercised end-to-end.

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