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

src/dto.rs

@@ -28,6 +28,14 @@ pub struct ParamDeclarationDto {
     /// See `crate::data_value::ParamDeclaration::auto_derived`. The frontend uses this to disable
     /// editing — `POST /api/params` also rejects a request naming an auto-derived param.
     pub auto_derived: bool,
+    /// Set only for the built-in `ottyl_seq`/`ottyl_ts`/`ottyl_fmt` names
+    /// (`crate::engine::OTTYL_RESERVED_PARAM_NAMES`), synthesized into the `GET /api/params`
+    /// response by `crate::api::list_params` rather than backed by any index entry — distinct from
+    /// `auto_derived` (which *is* a real, if machine-discovered, `ParamDeclaration`). Always
+    /// `false` for every other entry. There is no removal path for these at all (not just a
+    /// disabled one), so the frontend should treat `reserved` as non-deletable/non-editable.
+    #[serde(default)]
+    pub reserved: bool,
 }
 
 #[derive(Debug, Clone, Serialize)]