[docs] Document Aspire skills bundle fallback in aspire agent init

[aspire-repo-bot]

Documents changes from microsoft/aspire#17537 by @IEvangelist.

Targeting release/13.4 — the latest release branch on microsoft/aspire.dev — because release/13.5 (from the source PR milestone 13.5) does not exist there.

Why this PR is needed

PR microsoft/aspire#17537 changed aspire agent init (and the chained aspire new/aspire init flow) to use best-effort behavior when acquiring the Aspire skills bundle. Instead of failing with a non-zero exit code when the GitHub release asset is unavailable, the command now falls back to an embedded snapshot and, if that also fails, warns and skips only the bundle-backed skills. The existing docs described the command as always downloading skills from GitHub, leaving users in restricted-network or air-gapped environments without guidance.

Changes made

Updated src/frontend/src/content/docs/reference/cli/commands/aspire-agent-init.mdx:

• Added a new "Aspire skills bundle acquisition" subsection under the Description that explains the three-level resolution order:
  1. Existing validated cache
  2. GitHub release asset (with artifact attestation verification)
  3. Embedded CLI snapshot (offline/air-gapped fallback)
• Documented the best-effort behavior: when all sources fail the command warns and skips bundle-backed skills rather than exiting non-zero.
• Noted that aspire new and aspire init chained flows follow the same behavior.

Generated by PR Documentation Check for issue #17537 · ● 9.8M · ◷