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/file_remove_error_test.go

@@ -72,7 +72,7 @@ func TestFileRemoveAPIError(t *testing.T) {
 }
 
 // The unwritable answer must name the DIRECTORY. Removal needs write access to
-// the parent, so a message naming the file would send the operator to fix the
+// the parent, so a message naming the file would send an admin to fix the
 // wrong permissions. The directory is a prefix of the file path, which is why a
 // plain "contains the directory" check could never catch that regression.
 func TestFileRemoveAPIError_NotWritableNamesTheDirectoryNotTheFile(t *testing.T) {