Break the taskLearning metrics <-> routing static import cycle

[atomantic]

Problem — server/services/taskLearning/metrics.js and taskLearning/routing.js statically import each other, so they form a two-module ESM cycle. In a static cycle whichever member evaluates first sees undefined for the other's bindings; any top-level const derived from one of those imports becomes a boot-time TDZ crash the moment module ordering shifts.

The edges

// taskLearning/metrics.js:31
import { deriveFailureSignalAvoidance, isNonRoutableLearnedTier } from './routing.js';
// taskLearning/routing.js:13
import { resetTaskTypeLearning } from './metrics.js';

Plan — pick the smaller side and extract it to a leaf both can import. resetTaskTypeLearning is the single symbol routing.js needs, so move it (with whatever store access it needs) into a leaf — taskLearning/reset.js or the existing store module — and have both files import the declaring module. Do not fix this with await import(): a deferred import dodges the guard rather than removing the cycle.

Tests — delete this component's entry from KNOWN_CYCLIC_COMPONENTS in server/services/serviceImportCycles.test.js. That suite fails if the entry is left behind, so the baseline can only shrink.

Related to #5693