[BUG] Entire marketplace offline, all plugins unavailable on startup — silently fails due to non-graceful schema validation

When claude-plugins-official is fetched on startup, a ConfigParseError is thrown if any plugin entries fail schema validation, causing the entire marketplace to fail to load — including all entries that passed validation. The user sees only "Failed to install Anthropic marketplace · Will retry on next startup" with no indication of the underlying cause.

Expected behavior: Invalid entries should be skipped with a per-entry warning, and valid plugins should still be installed/loaded. This would also make the system resilient to future marketplace/client version skew, where newer source types are added to the marketplace before the client's schema is updated.

Versions affected: v2.1.22 and v2.1.77, both native installer and npm (macOS)

Error:
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ConfigParseError: Invalid schema: plugins.56.source: Invalid input, plugins.63.source: Invalid input, plugins.67.source: Invalid input, plugins.71.source: Invalid input, plugins.72.source: Invalid input, plugins.73.source: Invalid input, plugins.74.source: Invalid input, plugins.75.source: Invalid input, plugins.81.source: Invalid input
\\\

Related: #33068, #14360, #21687