feat: bound CLI input size for large files

[tappe9]

Summary

Implement Issue #37 as the first staged large-file hardening step.

• add a default 256 MiB CLI encoded-input limit;
• add --max-input-bytes <BYTES> as an explicit override;
• reject over-limit files with structured CliError::InputTooLarge before parsing;
• use file metadata for early rejection and cap the actual read at one byte beyond the limit to catch files that grow while being read;
• keep inspect(&[u8]) and inspect_with_limits() unchanged;
• document current in-memory behavior and the separation between input-byte limits and metadata-count limits.

Design

This intentionally does not add inspect_reader or a streaming/event API. Streaming/file-backed inspection remains a later library design, consistent with ADR 0003. Parsing stays entirely in the zstdscope library; the CLI only owns file-reading/resource policy and presentation.

Validation

TDD was used for the boundary behavior:

• RED: CI run #131 failed the four new large-file boundary tests before implementation while existing tests remained green.
• GREEN: the implementation made the boundary tests pass.
• Final CI run #133 passes format, clippy, workspace tests, rustdoc, core default-feature tests, package listing, publish dry-run, MSRV Rust 1.85.0, and Linux/macOS/Windows test jobs.

Closes #37