test(windows): add red regressions for platform-specific failures

[Flipper1994]

Summary

Adds Windows-only red tests and analysis for native Windows failures found during
a Windows red-test campaign. This PR intentionally contains no production
fixes — the tests are regression guards for follow-up maintainer fixes.

All tests reproduce at the product surface (a real codebase-memory-mcp.exe
process, real JSON-RPC stdio / CLI / HTTP UI, real SQLite DB), are deterministic,
use only the Python standard library, and pass on Linux/macOS.

Red test classes

• Smoke: 0
• Integration: 4
• Unit: 0
• Invariant: 0

(The wider campaign ran smoke/integration/unit/invariant attempts across
PowerShell 5.1, cmd.exe, Git Bash, direct Win32, Python subprocess, and
Python stdio; seed areas that behave correctly on Windows are listed as
"ruled out" in the analysis rather than shipped as tests.)

windows_non_ascii_repo_path_preserves_definitions (#636, #357)

Byte-identical TypeScript fixtures under non-ASCII parent paths (Latin-1 accents,
Cyrillic, CJK, Greek) extract zero definitions and only File/Folder nodes
(5/4) versus the ASCII baseline (12/20/5). The pipeline source readers
(read_file() in pass_definitions.c, pass_calls.c, pass_parallel.c,
pass_semantic.c, …) fopen() a UTF-8 path, which the Windows CRT reads in the
ANSI code page; discovery already uses the wide API, so files are listed but never
parsed.

windows_cli_non_ascii_repo_path_is_honored (#423, #20)

The cli index_repository entrypoint rejects a non-ASCII repo_path
("repo_path is required") because main() does not read the wide command line.

windows_hook_augment_emits_context (#618)

codebase-memory-mcp hook-augment (the PreToolUse Grep/Glob augmenter) emits
empty stdout for every payload on Windows. src/cli/hook_augment.c gates on
POSIX-style absolute paths (cwd[0] == '/' and the walk-up loop's
dir[0] == '/'), which a Windows drive-letter cwd never satisfies. A control
search_graph confirms the symbol is indexed.

windows_ui_picker_reaches_all_drives (#548)

The UI directory picker's GET /api/browse?path=/ returns no entries and never
enumerates logical drives, so drives other than the system drive (D:\, E:\)
cannot be selected. handle_browse in src/ui/http_server.c uses opendir
without a GetLogicalDriveStrings root case. Needs a UI build (cbm-with-ui)
and >1 drive; otherwise it reports a precondition (exit 2).

Related issues

Closes none. Reproduces or expands: #636, #357, #423, #20, #618, #548, #530.

Ruled out as green on Windows (documented in the analysis, no test shipped):
#513/#530.1/#635 (stdio handshake/flush), #422/#348 (search_code via
Select-String), #274 (ignore files), #371/#137 (detect_changes), #627
(query_graph), #272 (shell metachars), #511/#530.3 (non-UTF-8 → U+FFFD),
#331 (root containment), #185/#406 (process exit), #227/#367 (mapped subst
drive). Out of scope as cross-platform: #571, #530.2, #530.4, #530.5.

Windows environments tested

• OS: Microsoft Windows 11 Pro, build 10.0.26200
• Shells/clients: PowerShell 5.1, cmd.exe, Git Bash (MSYS2), direct Win32,
  Python subprocess.Popen, Python stdio JSON-RPC transport, embedded HTTP UI
• Filesystems/path shapes: NTFS; drives C: / D: / E: and a subst mapped
  drive; ASCII, Latin-1, Cyrillic, CJK, Greek segments; spaces, &, (), [],
  #, %, !, apostrophe; mixed slash/backslash; lower-case drive letters
• Locale/code page: 65001 (UTF-8 console)
• CBM source commit: b075f05; production + UI builds via make -f Makefile.cbm

How to run

pwsh -File scripts/test-windows.ps1
# the UI drive-picker test additionally needs a UI build:
#   make -f Makefile.cbm cbm-with-ui

Each test exits 0 (green), 1 (red / Windows failure reproduced), or 2
(precondition not met). Full environment, commands, ruled-out seed areas, and
suspected fix locations are in tests/windows/RED_TEST_ANALYSIS.md.

Expected maintainer action

Use these failing tests as regression guards while fixing the Windows path and
platform handling in follow-up PRs (route per-pass file reads through
cbm_utf8_to_wide + _wfopen; read the wide command line in main(); accept
drive-letter paths in hook_augment.c; enumerate logical drives in
handle_browse).

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