docs: api comments say what the endpoints do, not how they came to be (#6277)

Rewrites the internal/api comment blocks to rule 32: task, milestone and
rule ids gone, the stories behind them restated as the constraint they
left, stale references corrected (the stream secret is wired from config,
the timezone handler already refreshes the scheduler, the Android app is
the native client, the design docs cited are not in the repo). Also
rewraps comment lines over 80 columns left by the earlier batches.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/me_recommendation_metrics.go

@@ -21,7 +21,7 @@ const (
 	recMetricsLowVolume = 20
 )
 
-// Surface intents (milestone #127): each family is judged against its
+// Surface intents: each family is judged against its
 // job, not one global bar — discovery mixes are EXPECTED to run higher
 // skip rates than the go-to surfaces.
 const (
@@ -40,15 +40,15 @@ type surfaceMetric struct {
 	AvgCompletion float64 `json:"avg_completion"` // mean completion ratio, [0,1]
 	LowConfidence bool    `json:"low_confidence"` // plays < recMetricsLowVolume
 	// SkipDelta / CompletionDelta are this row's difference from the manual
-	// baseline WITH its margin of error (#2495). nil on the baseline row
+	// baseline WITH its margin of error. nil on the baseline row
 	// itself, and whenever the samples are too thin for a margin to mean
 	// anything. Computed server-side so both clients read the same arithmetic
-	// instead of each re-deriving it — and so `low_confidence` is no longer
-	// mistaken for a decision threshold, which it never was.
+	// instead of each re-deriving it. `low_confidence` is a display
+	// threshold, not a decision one.
 	SkipDelta       *metricDelta `json:"skip_delta,omitempty"`
 	CompletionDelta *metricDelta `json:"completion_delta,omitempty"`
 	// Breakdown splits the family into the pick-kind populations its
-	// builder stamped (#1249, generalized #1270): For You's taste/fresh,
+	// builder stamped: For You's taste/fresh,
 	// Discover's buckets, tier1-3 for tiered mixes — plus earlier plays
 	// that predate attribution. Present only when the family has at
 	// least one attributed play; the parent row remains the sum of its
@@ -128,7 +128,7 @@ type familyAccum struct {
 	// reduces to a single weighted division at the end.
 	completionSum float64
 	// completionSqSum is the sum of squared completion ratios, which is what
-	// makes the variance mergeable across raw source rows (#2495). Standard
+	// makes the variance mergeable across raw source rows. Standard
 	// deviations cannot be combined; sums of squares add exactly.
 	completionSqSum float64
 }