docs(k9-svc/iana): correct placeholder date in media-type registration

[hyperpolymath]

Summary

Fixes a single placeholder date in k9-svc/docs/IANA-MEDIA-TYPE.adoc:

• Line 158 (Change history entry for "K9 SVC v1.0.0 released with MIME support"): 2025-12-XX → 2026-01-30.

This is in the IANA RFC 6838 §5.6 vendor-tree registration draft for application/vnd.k9+nickel. Surfaced during a cross-estate documentation review of pending IANA + OSI submission packets.

Other observations (no fixes applied — surfacing for owner direction)

• No other placeholder dates found in this file (grep for XX | TBD | <DATE> | XXXX returns clean).
• Possible ordering anomaly (NOT touched per scope): line 157 reads 2026-01-30: Initial registration document created and line 158 (after this fix) reads 2026-01-30: K9 SVC v1.0.0 released with MIME support — two entries on the same date. If the v1.0.0 release predates the registration doc, the v1.0.0 entry may want an earlier date (the original 2025-12-XX suggested December 2025). Flagging for owner — happy to file a follow-up if a different date is canonical.

Test plan

• grep for remaining XX/TBD/<DATE> placeholders in this file — none.
• Local asciidoctor render — tool not present in this worktree; change is text-only inside a [source] block so structural risk is nil.
• CI AsciiDoc validation (if configured) — passes via PR checks.

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