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/admin_coverage.go

@@ -39,11 +39,12 @@ func (h *handlers) handleGetLibraryCoverage(w http.ResponseWriter, r *http.Reque
 	})
 }
 
-// fingerprintCoverageResp is the wire shape for GET /api/admin/library/fingerprints.
-// fingerprinted + rejected + pending = total. Missing tracks are not counted:
-// there is no file to fingerprint. Enabled travels with the counts because with
-// fingerprinting off (#3913) pending never shrinks, and a gauge that implies
-// progress would be promising work nothing is doing.
+// fingerprintCoverageResp is the wire shape for GET
+// /api/admin/library/fingerprints. fingerprinted + rejected + pending = total.
+// Missing tracks are not counted: there is no file to fingerprint. Enabled
+// travels with the counts because with fingerprinting off pending never
+// shrinks, and a gauge that implies progress would be promising work nothing is
+// doing.
 type fingerprintCoverageResp struct {
 	Total         int64 `json:"total"`
 	Fingerprinted int64 `json:"fingerprinted"`
@@ -70,7 +71,7 @@ func (h *handlers) fingerprintCoverage(ctx context.Context) (fingerprintCoverage
 }
 
 // handleGetFingerprintCoverage implements GET /api/admin/library/fingerprints:
-// how far the fingerprint backfill (#3908) has got. The backfill is its own
+// how far the fingerprint backfill has got. The backfill is its own
 // worker spanning many passes, with no scan run to attach a tally to, so its
 // progress is read live here. Always 200; zeros on an empty library.
 func (h *handlers) handleGetFingerprintCoverage(w http.ResponseWriter, r *http.Request) {