docs: align MISSION.md cross-reference with established-TLP framing

[NekomyaDev]

Fixes #1006.

The Cross-references entry still called MISSION.md a draft project-establishment proposal, contradicting line 48 ("the founding mission of the established TLP") and the status banner in MISSION.md itself (established by ASF Board resolution on 17 June 2026; the original proposal kept as a historical record).

One-line change: the entry now matches both, and still tells the reader what is inside (motivation, scope, design commitments, initial PMC composition target).

Docs-only single-line edit; relying on PR CI for the prek pass.

[potiuk]

Thanks for catching this — the line is genuinely stale, and your replacement is well grounded: it is close to verbatim from MISSION.md's own banner ("the original establishment proposal, kept as a historical record"), which is exactly the right source to align against.

The catch is ownership rather than content: #1019 changes this identical line with the same intent and was opened first. Both branches start from the same README.md blob, so they conflict by construction — only one can land. I have approved that one, which means this PR is heading for a close-as-duplicate rather than a merge. That is first-come on an identical edit, not a judgement on your change.

Smaller observations

• README.md:238 — independent of the duplicate question, worth knowing for next time: the bullet already opens with an em-dash separator, so adding a second one mid-sentence leaves the line carrying two em dashes plus a colon. AGENTS.md § Writing and editing documentation asks that contributors "Use em dashes sparingly" and "Prefer small, targeted edits over rewrites" — the shorter form keeps the surrounding list rhythm intact.

Your other open PR, #1032, touches different files and is unaffected by this. Thanks for both — please do keep them coming.

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[potiuk]

Closing as a duplicate of #1019, which edits the same README.md line and was opened first — see the review above for the detail. Thanks again for spotting the stale wording; your other PR, #1032, is unaffected.