Windows path handling in PathNormalizer + Windows e2e runner

[jleni]

Summary

Two coupled gaps that should land together so the implementation has its test backing on day one.

What's missing

PathNormalizer Windows support

Current `PathNormalizer::normalize` and `remap_args` are byte-literal `String::replace`. On Windows that breaks in three ways:

1. Separator mismatch. PathNormalizer's canonicalized prefix uses `\` (Windows path); rustc dep-info often reports paths with `/`. Literal-replace finds no match → leak.
2. Drive-letter case. `C:\` vs `c:\` are the same NTFS path; `String::replace` is case-sensitive.
3. Missing standard prefix sentinels. Windows dev paths live under `%USERPROFILE%` (covered via `dirs::home_dir`), but also `%APPDATA%`, `%LOCALAPPDATA%`, `%PROGRAMFILES%`. None are in the rule list today.

Windows e2e runner

`.github/workflows/ci.yml` has a `windows-check` exploratory job that only does `cargo check --target x86_64-pc-windows-msvc`. The harness (`crates/kache-e2e`) doesn't run on Windows at all, so:

• Path-handling code lands without real validation
• Future regressions on Windows are invisible until a user reports them
• The newly-merged Task Scheduler support (feat(windows): add Task Scheduler support for daemon install #76) has no e2e coverage either

Proposed fix

• Add separator + case normalization in `PathNormalizer`'s prefix matching (canonicalize to `/` and lowercase the drive letter at construction).
• Add ``, ``, `` rules in `from_env` when running on Windows.
• Stand up a Windows runner in CI and run the existing e2e harness on it. Both the new Windows path code and existing fixtures get validated.

Why bundled

Landing the implementation without Windows e2e weakens the test-first invariant the rest of the path-handling work has been built on. Pair them.

[emmanuelm41]

Done — both halves shipped and now validate each other on the Windows e2e arm (green & blocking).

PathNormalizer Windows support (src/path_normalizer.rs):

• Separator + drive-case handled via per-rule variants (push_rule_with_variants: forward-slash + lowercase_drive_letter).
• <APPDATA> / <LOCALAPPDATA> / <PROGRAMFILES> sentinels added in from_env.
• The missing piece that made any of it actually fire on Windows: canonical_string now strips the \\?\\ verbatim prefix (feat(windows): green & blocking e2e, cache-key path-independence fixes, and an MSVC release binary (#201, #202, #203) #209) — without it every rule prefix was \\?\\C:\\… and never matched the plain paths cargo/rustc emit, so OUT_DIR leaked into the cache key.

Windows e2e runner: the kache-e2e harness runs on the self-hosted Windows runner, now blocking (#82, #209). All 15 fixtures pass — including the relocate path-independence test that directly exercises the PathNormalizer Windows handling above.

Closed by #209 (merged). Remaining nice-to-haves are out of scope here: Windows mentions in configuration.mdx/daemon/lifecycle.mdx docs, and e2e coverage for the Task Scheduler service (#76).