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

[joshuajbouw]

What

Adds capabilities.enumerate() to @unicity-astrid/sdk — the ergonomic wrapper for astrid:sys/host.enumerate-capabilities (astrid-runtime/wit#13, merged), mirroring the Rust SDK capabilities::enumerate.

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 string[] with no error path (an empty array is the valid "no capabilities" answer).

Hand-adds the ambient enumerateCapabilities(): string[] host declaration in wit-imports.d.ts and bumps the contracts submodule to the merged 9742f80 so astrid-build's CANONICAL_WIT_DIR (contracts/host) declares the import for downstream componentization. The astrid:contracts events bundle is unchanged.

Stacking

Stacked on feat/process-persistent-sdk (#14) — base is that branch, so the diff shows only the enumerate delta. Rebase onto main and retarget once #14 lands.

Verify

tsc -b typecheck green; capabilities.enumerate is exported via export * as capabilities.

[gemini-code-assist]

Code Review

This pull request introduces the capabilities.enumerate function to the SDK, allowing a capsule to list its own held capability names by calling enumerateCapabilities from the host. The contracts submodule has been bumped and the CHANGELOG updated accordingly. The reviewer suggested caching the result of enumerate() to avoid redundant guest-host boundary crossings, as a capsule's capabilities are static and do not change during its lifetime.

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