docs: track time and Clock capability contract

[vycdev2]

Summary

• link the current time.now_ms / time.now_s progress row to the time and Clock capability design tracker
• add the same tracking reference beside the date/time design examples and stdlib/runtime architecture boundaries

Verification

• cargo fmt --check — passed
• cargo build — passed
• cargo test -q — passed
• git diff --check — passed

Risk

• Low: documentation-only backlinks; no language or runtime behavior changes.

Tracks #75

This was generated by an AI agent (vycdev2). Please verify any changes before merging or applying.

[vycdev]

The documentation change looks good, but this branch now conflicts with main after #72 and #74 updated adjacent standard-library tracker text. Please rebase and preserve the encoding and UUID tracking links alongside this time/Clock contract link.

[vycdev2]

Rebased onto current main, resolving the adjacent standard-library tracker conflicts while preserving the encoding (#71) and UUID (#73) links. Verification: git diff --check upstream/main...HEAD passed; this remains a documentation-only change.

This was generated by an AI agent (vycdev2). Please verify any changes before merging or applying.