fix(wiki): canonicalize whitespace across a whole section, not just its ends

Review of PR #129 found MergeReport's disagreement check compared
strings.TrimSpace(sA.content) against strings.TrimSpace(sB.content) --
only leading/trailing whitespace is tolerated. Every other content
comparison in this file (appendNew, mergeBullets) already canonicalizes
internal whitespace runs too, because a re-extraction's exact spacing
isn't byte-stable (#103). A mid-line double-space would false-positive
as a "disagreement" here even though the file's own established
tolerance says it shouldn't.

canonicalBlock applies the existing canonicalLine per line of a
multi-line section body. A genuine content difference is still caught
(TestMerge_ReportsSectionsWhereTheFreshVersionWasDiscarded stays green);
only internal-whitespace-only variants stop false-positiving.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

ingestion/internal/wiki/merge.go

@@ -84,7 +84,7 @@ func MergeReport(a, b Page) (Page, []string) {
 			secsA[i].content = appendNew(sA.content, sB.content)
 		default:
 			// a wins — but say that b disagreed, rather than dropping it mute.
-			if strings.TrimSpace(sA.content) != strings.TrimSpace(sB.content) {
+			if canonicalBlock(sA.content) != canonicalBlock(sB.content) {
 				conflicts = append(conflicts, sB.heading)
 			}
 		}
@@ -329,6 +329,21 @@ func canonicalLine(line string) string {
 	return strings.Join(strings.Fields(line), " ")
 }
 
+// canonicalBlock applies canonicalLine per line of a multi-line section body
+// — the same whitespace-insensitivity appendNew/mergeBullets already give a
+// single line, extended to a whole section for MergeReport's disagreement
+// check (found in review, PR #129: comparing raw strings.TrimSpace only
+// tolerated leading/trailing whitespace, not a re-extraction's mid-line
+// spacing, which every other comparison in this file already tolerates).
+func canonicalBlock(block string) string {
+	lines := strings.Split(block, "\n")
+	out := make([]string, len(lines))
+	for i, l := range lines {
+		out[i] = canonicalLine(l)
+	}
+	return strings.Join(out, "\n")
+}
+
 // appendNew concatenates the lines of b that a does not already carry.
 //
 // Append sections used to concatenate wholesale, which is correct exactly once.