Add empty-trash command, config-file roots, and scan --root

[UnbreakableMJ]

Summary

Three user-requested capabilities for the disk cleaner, plus the agent/doc surface to match.

• vacuum empty-trash — a new flat-verb subcommand that permanently empties the OS trash, completing the clean → trash → reclaim loop. Dry-run by default (lists items + a lower-bound reclaimable-bytes figure), --apply to purge, --yes/--force for non-interactive use, confirmation prompt, live spinner, and the standard JSON/JSONL/Human envelope. Platform-gated via the trash crate's os_limited module (Linux/Windows); other targets return a structured UNSUPPORTED_PLATFORM error. The backend reports no byte size for trashed directories, so the total is shown as "at least …" and the number of uncounted directories is surfaced (item count is always exact).
• Config-file roots (TOML) — optional ~/.config/vacuum/config.toml with roots = ["~/projects", …] so default scan directories persist. Precedence: CLI --root/paths > VACUUM_ROOTS env > config roots > $HOME, via a new --config/VACUUM_CONFIG global. vacuum-core stays pure — all config logic lives in vacuum-cli (config.rs). Unknown TOML keys are ignored for forward-compat; an explicitly named missing --config file is a usage error (exit 2).
• scan --root — scan now accepts --root (merged with positional paths) for parity with list/clean.

Surface & docs

• schema / describe advertise empty-trash.
• Texinfo manual: new empty-trash subcommand, --config, and a Configuration chapter (builds zero-warning).
• AGENTS.md and SKILL.md updated (commands, config precedence, env vars).

Testing

• cargo fmt --check · cargo clippy --workspace --all-targets -- -D warnings · cargo test --workspace (39 pass — 6 new config unit tests, 4 new integration tests) · reuse lint compliant · makeinfo zero-warning.
• Manual end-to-end: dry-run trash listing (purges nothing), config + VACUUM_ROOTS + --root precedence, and --config <missing> → exit 2 all confirmed.

Notes

• Interactive TUI directory picker was scoped out of this round (deferred to its own ~3–4 day effort).
• Config is intentionally roots-only for now; the Config struct is left extensible.

🤖 Generated with Claude Code