docs(agents): fix self-contradicting customize.toml headers

[gmoncor]

What: Replace the "DO NOT EDIT ... Customize the persona and menu below" header in the 5 agent customize.toml files with the non-contradictory header already used elsewhere in the repo.

Why: The current header tells the reader not to edit the file and then immediately tells them to customize it below, which is self-contradicting and inconsistent with the pattern already used by non-agent skills (bmad-brainstorming, bmad-prd).

How:

• Copy the header wording from skills/bmad-brainstorming/customize.toml, including the explicit override-file paths block.
• Apply identically to all 5 agent customize.toml files.

Testing: Read-through diff confirming identical, consistent header text across all 5 files; doc-only change, no executable code involved.

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