fix: Windows CI - use path not filepath for GitHub URL paths

[thecodeassassin]

Problem

test (windows-latest) failed on main (run 27534675029, merge of #21):

--- FAIL: TestFetchGitHubBlobSkillMdFetchesContainingDirectory
    skills_test.go:209: Fetch failed: fetching GitHub directory: unexpected URL:
    https://api.github.com/repos/sveltejs/ai-tools/contents/tools\skills\svelte-core-bestpractices?ref=main

internal/skills/fetch.go used path/filepath (filepath.Dir/Base/Ext) on URL paths. On Windows filepath uses \ as separator and cleans paths to backslashes, corrupting the GitHub API URL. Passes on Linux/macOS because their separator is /.

Fix

Use the path package (always /) for URL path manipulation; keep path/filepath for local filesystem paths only.

Verification

• go test ./... green
• go vet ./... clean
• golangci-lint: no issues on changed file

[github-actions]

Merging this branch will not change overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/Cloud-Exit/ExitBox/internal/skills	0.00% (ø)

---

Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/Cloud-Exit/ExitBox/internal/skills/fetch.go	0.00% (ø)	0	0	0

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.