feat(sdk): add capabilities::enumerate for sys enumerate-capabilities

[joshuajbouw]

What

Adds capabilities::enumerate() to astrid-sdk — the ergonomic wrapper for astrid:sys/host.enumerate-capabilities (astrid-runtime/wit#13, merged), implemented kernel-side in unicity-astrid/astrid (feat(sys): implement enumerate-capabilities + complete check-capsule-capability).

It is the infallible list dual of capabilities::check: returns the calling capsule's own held capability names — the categories declared in its [capabilities] manifest block (host_process, net_connect, fs_read, …), not the scoped arguments within them. Argument-free, returns Vec<String> with no error path (an empty list is the valid "no capabilities" answer), so a reusable capsule can ground its behaviour in what it can actually do instead of hard-coding it.

The contracts submodule is bumped to the merged 9742f80 so astrid-sys regenerates the binding; astrid-sys/wit-staging restaged.

Stacking

Stacked on feat/process-persistent-sdk (#53) — base is that branch, so the diff shows only the enumerate delta. Rebase onto main and retarget once #53 lands.

Verify

cargo build --workspace and cargo clippy --workspace --all-targets green.

[gemini-code-assist]

Code Review

This pull request introduces capability introspection by adding the capabilities::enumerate function (and the underlying enumerate-capabilities WIT function) to list the calling capsule's own held capability names. The feedback identifies an issue with the intra-doc links [check] and [enumerate] in the capabilities module documentation, which will fail to resolve and should be fully qualified as [capabilities::check] and [capabilities::enumerate].

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