Policy: protectedHeaders needs byte-string matching and array quantifiers

protectedHeaders ships with text and int scalar matchers. Two things it cannot express:

1. Byte strings. A bstr header can be addressed but no matcher applies, so certificate thumbprints and key identifiers are not pinnable. render_scalar truncates a bstr to its first 16 bytes, so matching must be on real bytes, not the rendering.

2. Arrays. A path can index one element ([34, 0]), but there is no way to say "any element" or "every element".

The motivating shape is the Azure Artifact Signing external-signatures proposal: a text label whose value is an array of maps, each re-using COSE labels 1 (alg), 4 (kid), 33 (x5chain), 34 (x5t = [hashAlg, hashValue]), -1 (raw signature).

Design constraints already committed to:

• * is refused at parse time today and is reserved for this.
• match: "all" over an empty array must not pass vacuously.
• Matchers must stay type-declared; matching on render_scalar output is a type-confusion vulnerability.

Start by tracing protectedHeaders parsing and matching, including render_scalar, and inspect how indexed paths are handled. Confirm the existing refusal of * and the scalar type declarations before designing byte-string and array-quantifier behavior. Done means byte matching uses actual bytes, any/all handle empty arrays as specified, and render_scalar is not used for matching.