Make ottyl_seq/ottyl_ts usable in dashboard PromQL queries (ticket 055)

evaluate_promql previously resolved every metric name through bucket_values,
which only returns data for a real MetricDeclaration — so a dashboard panel
querying ottyl_seq/ottyl_ts/ottyl_fmt (already supported in the filter bar
and alert conditions) silently returned an empty series. ottyl_seq/ottyl_ts
are now synthesized directly from the ingested-log index instead of requiring
a declaration; ottyl_fmt is categorical (json/logfmt/none) with no sensible
numeric reading, so it's rejected up front with a clear error pointing back
at the filter bar rather than returning nothing.

GET /api/params now also lists the three reserved names (marked `reserved:
true`, distinct from `auto_derived`) purely for discoverability — merged in
at the API layer only, not the engine's internal ParamDeclarations query, so
profile-switch removal and metric-param-promotion logic are unaffected.
declare_param also now rejects declaring a param under one of these names.

Docs.tsx and the Params panel are updated to reflect the new dashboard
support and the reserved/non-editable listing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

webapp/src/components/Docs.tsx

@@ -105,6 +105,9 @@ const SECTIONS: DocSection[] = [
           <Code>ottyl_seq</Code>, <Code>ottyl_ts</Code>, and <Code>ottyl_fmt</Code> are reserved metric names present
           on every log line, so they're always filterable without declaring anything. <Code>ottyl_fmt</Code> holds the
           auto-detected format of the line's text — <Code>json</Code>, <Code>logfmt</Code>, or <Code>none</Code>.
+          They also appear (flagged <Code>reserved</Code>) in <Code>GET /api/params</Code> for discoverability, though
+          there's no UI to edit or remove them — see also <em>Dashboards</em> below for using{' '}
+          <Code>ottyl_seq</Code>/<Code>ottyl_ts</Code> in a panel query.
         </p>
         <p className="font-semibold text-text">Date/time formats</p>
         <p>Timestamp comparisons accept three forms:</p>
@@ -335,6 +338,14 @@ const SECTIONS: DocSection[] = [
           Dashboards are saved per profile, so they travel with it when you switch or copy it — an active profile is
           required to create or save one; pick or create one from the settings menu first.
         </p>
+        <p>
+          The reserved <Code>ottyl_seq</Code>/<Code>ottyl_ts</Code> names (see <em>Filtering</em> above) work in panel
+          queries the same as any declared metric — e.g. <Code>count(ottyl_seq)</Code> for log volume, or{' '}
+          <Code>rate(ottyl_ts[1m])</Code> for ingest rate — since every log line carries them without a metric
+          declaration. <Code>ottyl_fmt</Code> is categorical (<Code>json</Code>/<Code>logfmt</Code>/<Code>none</Code>
+          ), not a number, so it's rejected in a panel query with an explicit error rather than silently charting
+          nothing — filter on it in the filter bar instead.
+        </p>
       </div>
     ),
   },