Fix lint suppressed by mcp's deferrals and prune dead root deferrals

[williamthorsen]

Problem

packages/mcp/ defers four unicorn rules to warn, suppressing 11 violations. Separately, three rules deferred at the repo root no longer have any violation to justify them.

Proposed solution

Fix mcp's violations and remove its deferral scaffolding outright, rather than leaving an empty list behind. Prune the dead root entries.

Acceptance criteria

Must have

• packages/mcp/ is clean with these four rules at their default error severity: unicorn/no-top-level-assignment-in-function, unicorn/no-unnecessary-splice, unicorn/prefer-await, unicorn/prefer-unicode-code-point-escapes.
• mcp declares no lint deferrals: packages/mcp/.config/ is gone, and no mcp config references a deferral list.
• The root deferral list retains only rules that still have violations.
• Every other package's lint and strict-lint results are unchanged.
• Behavior changed while clearing the violations stays covered by tests.
• nmr ci passes.