OpenViking v0.3.3 expects directory URIs for abstract/overview reads.
Passing pseudo-files like /.overview.md and /.abstract.md to
/api/v1/content/overview|abstract triggers HTTP 500.
This change normalizes those pseudo-URIs to their parent directory for
abstract/overview requests, preserves full reads, and hardens parsing for
wrapped/unwrapped result payloads and fs list response shapes.
97a851bf97