auth.ts: dropped the legacy HS256-shared-secret verification path, keeping
only the JWKS path Supabase recommends now — one code path instead of two.
Also fixes a real bug: @types/bun's ambient types didn't resolve inside a
bun workspace (its internal 'bun-types' reference can't hoist into a nested
package's node_modules the same way it does in a flat install). Depending on
bun-types directly instead of @types/bun fixes it — verified with a clean
'bun run typecheck'.
parse_header now only handles '; key = value' lines instead of three
different slicer comment formats at once. Error enum trimmed from 4
variants to 3 (Io, Parse, Other).
Verified with cargo test (3/3 passing).
octoturge