Adds read-extraction for Xbox 360 STFS container packages

[rdmrocha]

STFS extraction

• Added xtafkit extract-stfs <PACKAGE> for streaming Xbox 360 STFS containers (CON / LIVE / PIRS) to a local directory. --to <DIR> overrides the destination; --dry-run lists the entries with sizes and totals; --json emits machine-readable output for both dry-run and post-extract modes.
• Default destination (no --to) is ./<DisplayName>/ taken straight from the STFS header — no catalog lookup, no [TitleID] suffix. The per-package display_name is consistently more specific than the title-id catalog mapping (notably for XBLIG, where every indie game shares the same system title-id and the catalog can only return a generic bucket name).
• Read-only / type-1 STFS only. Type-0 (read-write, used by save games / on-drive system files / CON packages) surfaces an explicit "STFS type 0 (read-write) not supported yet" error rather than producing wrong output.
• Block-index → byte-offset translator handles all interleaved hash levels: L0 every 0xAA blocks, L1 every 0x70E4, L2 every 0x4AF768. Inline boundary tests pin offsets at 0xA9, 0xAA, 0x70E3, 0x70E4 against literal hex values and assert strict monotonicity across boundaries.
• File chain follower covers both the consecutive fast path (no hash-block reads) and the fragmented case (next-block pointer threaded through the L0 hash block at offset (N % 0xAA) * 24 + 0x15). Walk is capped at used_blocks iterations to reject malformed cyclic chains, mirroring the existing FAT cycle rejection in volume.rs.
• Defensive parent-chain resolution in extract_to_host: rejects cyclic parent_index references and out-of-range parent pointers; refuses to overwrite existing output files.

Library API additions

• New fatxlib::stfs submodules: volume_descriptor, block_translator, file_entry, extract. Existing header parsing (StfsHeader, parse_header, MIN_HEADER_BYTES) moved into fatxlib::stfs::header and re-exported at the namespace root — no breaking changes for existing callers.
• fatxlib::stfs::StfsPackage::{open, header, volume, entries, read_block_chain, read_file} — read API for STFS packages. read_file<W: Write> streams through a writer; no full-file buffering even for multi-hundred-MiB packages.
• fatxlib::stfs::extract::extract_to_host(&mut StfsPackage, &Path, Option<ProgressFn>) -> Result<ExtractReport> — top-level walk + write, with progress callback shape matching the existing XISO extract ((rel_path, file_size, total_bytes_so_far)).
• fatxlib::stfs::extract::ExtractReport — { files, directories, bytes } returned on success.

Testing / maintenance

• 27 inline synthetic tests across the four new STFS submodules: volume-descriptor parsing (type-0/1 detection, wrong-size rejection, truncation), type-1 block translator (boundary indices at every hash level plus monotonicity), file entry parsing (consecutive flag, directory flag, parent-index, non-ASCII tolerance), and end-to-end synthetic package extraction with a nested directory tree.
• v2 TUI extract-gating rule documented in the design spec: the future TUI sniff prompt will offer (X)tract only when the package contains a default.xex file (the only reliable signal that loose extraction produces something useful for alt-dashboards). Fallback: gate on content_type == 0x000D0000. The CLI extract-stfs is unrestricted.