feat(workers): add dedicated skill and complete billing ledger queries

[dxiongya]

Adds a standalone bundled xapi-workers skill for deployment, six managed resource types, real acceptance, consumption reconciliation, retention and environment-scoped cleanup. The skill keeps customer charges, platform funding, frozen funds and incomplete provider evidence separate, and documents test API routing and CI usage.

workers billing ledger --all now follows one snapshot across every page, preserves filters and page tracing IDs, and rejects repeated cursors, duplicate entries, changed scope/snapshot or the 100-page limit. Human overview output uses current customer accrual and platform funding fields while preserving older API compatibility and exact decimal strings. Single-page JSON output remains unchanged.

Validation:

• bun install --frozen-lockfile
• bun run typecheck
• bun run build
• bun run test: 393 passed, 0 failed
• npm pack --dry-run --ignore-scripts: all six standalone skill files included
• Skill validator and independent read-only scenario evaluation passed; resulting scope/freshness/cleanup clarifications incorporated.
• Real test API read-only query: 11 pages, 1,095 unique ledger entries; exact net $0.00064709 matched the same-snapshot overview. Provider quality remained INDETERMINATE; this does not establish final provider-invoice or storage-day reconciliation.

Base branch is feat/workers-platform, because this change extends its existing project commands/templates. This PR isolates the new skill and billing improvements; the underlying Workers feature still needs integration into the release branch. No version, release tag, npm publication, or live resource mutation is included.