docs: fix CoC contact link and CNCF name in CODE_OF_CONDUCT.md

[Priyanshubhartistm]

Why

CODE_OF_CONDUCT.md had two small but real problems in its contact line:

1. The private Maintainer mailing list link was missing the mailto: scheme, so instead of opening an email client it rendered as a broken/relative link. This is the same bug that was just fixed in governance.md (docs: fix broken maintainer mailing list links in governance.md #2244) - just in a different file.
2. "Cloud Native Foundation" is not a real organization - CNCF stands for Cloud Native Computing Foundation, and that's the name used correctly everywhere else in this repo (see README.md, governance.md).

What changed

• CODE_OF_CONDUCT.md: added mailto: to the maintainer mailing list link, and corrected "Cloud Native Foundation" to "Cloud Native Computing Foundation".

Open question / not addressed here

While looking at this I noticed the three docs that describe how to report a CoC violation each name a different secondary contact:

• README.md points to a named Linux Foundation mediator (Mishi Choudhary)
• CODE_OF_CONDUCT.md points to a generic CNCF email (conduct@cncf.io)
• governance.md points to an unnamed CNCF Code of Conduct Committee

I don't know which of these is actually current/correct, so I'm not guessing at a reconciliation here - this PR only fixes the mechanical link/name issues. Flagging in case a maintainer wants to pick one canonical contact path across all three files as a follow-up.

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