fix(fb-36): address PR #127 round 1 review

- ingested_after: convert OffsetDateTime to UTC before formatting
  so non-Z offsets compare correctly against UTC TEXT storage
  (lexical.rs + filters.rs)
- README: --tag is repeatable-only, not csv (only --media is csv)
- test(cli): add multi-value --tag OR-within IN-list coverage
- test(store): add UTC-offset regression test for ingested_after
- mcp: use ERROR_V1_ID const instead of hardcoded "error.v1"

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/kebab-search/src/lexical.rs

@@ -348,11 +348,15 @@ fn run_query(
 
     // p9-fb-36: ingested_after filter.
     // `documents.updated_at` is RFC3339 stored as TEXT (always UTC `Z` per
-    // fb-32 ingest path), so lexicographic >= compare is correct.
+    // fb-32 ingest path), so lexicographic >= compare is correct — but only
+    // when the filter instant is also formatted as UTC `Z`. A non-UTC offset
+    // (e.g. `+09:00`) would compare as ASCII after `Z` (0x2B < 0x5A) and
+    // produce wrong results. Convert to UTC before formatting.
     if let Some(after) = &filters.ingested_after {
         let formatted = after
+            .to_offset(time::UtcOffset::UTC)
             .format(&time::format_description::well_known::Rfc3339)
-            .expect("OffsetDateTime formats to RFC3339");
+            .expect("OffsetDateTime (UTC) formats to RFC3339");
         sql.push_str(" AND d.updated_at >= ?");
         params.push(Box::new(formatted));
     }