fix(windows): error on full index - use cmd.exe-compatible syntax (Fixes #324)

[hippus]

Previously on full index under Windows there is an error after step 5: The filename, directory name, or volume label syntax is incorrect.
This PR fixes cmd.exe syntax

[1/9] Building file structure
  Extracting: N/N files (100%))
[2/9] Extracting definitions
[3/9] Building registry
[4/9] Resolving calls & edges
[5/9] Detecting tests
[7/9] Analyzing git history
[8/9] Linking config files
[9/9] Writing database

[DeusData]

Thank you, @hippus! 🙏 Clean diagnosis of a real Windows blocker (#324). You're exactly right: cd '%s' && ... 2>/dev/null is POSIX-shell syntax — cmd.exe doesn't understand single quotes and /dev/null isn't a valid path, which is what produced "The filename, directory name, or volume label syntax is incorrect" right at the git-history step of a full index. Switching to git -C "%s" ... 2>NUL is the correct cross-platform form (and git -C is more robust than cd && even on POSIX).

Since the PR branch predated the :%%ct commit-timestamp field that was added to the pretty-format string (temporal-properties work, #257), it no longer applied cleanly to main, so I distilled your fix onto current main with that field preserved and credited you as the commit author:

Landed in df38e33, which closes #324. Verified locally: build clean, all 3,617 tests pass (githistory pass runs fine). I also confirmed the double-quoted path is safe — cbm_validate_shell_arg rejects ", $, backtick and backslash before the command is built. Thanks for making Windows better! 🪟