refactor(registry): fail-close on unexpected errors in loadInstanceContext/getFilterStats

[polaz]

Context

Found during review of #380.

Problem

loadInstanceContext() and getFilterStats() catch blocks swallow unexpected errors and fall back to "assume reachable / empty context". This can surface tools that the current instance cannot actually use when the error is not an initialization issue.

Suggested approach

Only swallow expected initialization errors ('not initialized', 'No instance'). For unexpected errors, either preserve the previous cache or bubble out.

Files involved

• src/registry-manager.ts (lines 303-323, 777-782)