fix(html):preserve fragment-only anchor links during path resolution (#3262)

fix(html): preserve fragment-only anchor links during path resolution

Fragment-only hrefs (e.g. href="#section1") were resolved as filesystem
paths when source_uri was set, breaking internal document navigation.

Add '#' to the skip-resolution prefixes in _resolve_relative_path() so
fragment links pass through unchanged.

Partially addresses #2929

Signed-off-by: aatrey56 <aatrey.sahay@gmail.com>