Extract fixpath core logic into dazzle-filekit

[djdarcy]

Extract fixpath core logic into dazzle-filekit

Problem

dz fixpath (in dazzlecmd) has path normalization and search logic that would be useful as a shared library. Currently it's a CLI-only tool -- other tools like dazzlelink can't reuse its path resolution capabilities.

Proposed solution

Extract core functions from dazzlecmd/fixpath.py into dazzle_filekit/pathfix.py:

• fix_path_string() -- normalize slashes, encoding, platform quirks
• probe_alt_platform() -- try MSYS, WSL, UNC path variants
• search_by_filename() -- fuzzy file search as last resort

dazzlecmd/fixpath.py becomes a thin CLI wrapper over dazzle_filekit.pathfix.
dazzlelink can then import the path normalization for the "both paths broken" rebase case.

Acceptance criteria

• dazzle_filekit/pathfix.py created with extracted functions
• dazzlecmd/fixpath.py refactored to use the library
• dazzlelink rebase uses pathfix as Case 4 fallback
• Tests for pathfix module
• Version bumps for dazzle-filekit and dazzlecmd

Related issues

• Refs Integrate dz fixpath for broken dazzlelink recovery #14 -- fixpath integration
• Refs Epic: Portable cross-references -- relative paths and fixpath integration #12 -- parent epic