React 19 requires `supportsMicrotasks: true` in the reconciler host
config so it can flush state updates from passive effects via
queueMicrotask. Without this, state updates triggered inside
useMcpConnectivityStatus were silently dropped, corrupting React's
internal executionContext and causing all keyboard input to freeze
after the "N MCP server(s) need auth" notification appeared.
Root cause (three-part fix):
1. reconciler.ts: declare supportsMicrotasks + scheduleMicrotask so
React 19 schedules passive-effect flushes correctly.
2. useMcpConnectivityStatus.tsx: wrap the MCP auth notification effect
in try/catch so any unexpected throw does not propagate into
flushPassiveEffects and permanently corrupt executionContext.
3. notifications.tsx: wrap addNotification, removeNotification, and
processQueue in try/catch for the same reason — these are called
from 12+ notification hooks across passive effects.
Also fixes a pre-existing test isolation bug in context.test.ts where
assigning `undefined` to process.env produced the string "undefined",
polluting the env for subsequent test files.
Resolves: #169, #205, #77
