fix: strip trailing slashes from base_path to prevent broken URLs
base_path values like "tedium.co/" combined with paths like "/some-post"
produce double-slash URLs ("https://tedium.co//some-post") that 404.
The trailing slash comes from publication URLs like "https://tedium.co/"
where stripUrlScheme preserved it. Fix in three places:
- tap.zig: stripUrlScheme strips trailing slash
- indexer.zig: HTTP fallback strips trailing slash
- indexer.zig: normalize base_path after all resolution (catches values
already stored in publications table with trailing slashes)
Backfill: RTRIM(base_path, '/') on both documents and publications.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>