Merge ticket 055: make ottyl_* reserved params usable in dashboard PromQL queries

Resolved conflicts with ticket 051's unknown-metric guard in evaluate_promql
(reordered so ottyl_fmt's categorical rejection and the reserved-name
skip both run before 051's declaration/bucket-data check, since
ottyl_seq/ottyl_ts are synthesized from the log index and never have a
MetricDeclaration or bucket entries) and merged both tickets' additions
to the reserved-params Docs.tsx paragraph.

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

webapp/src/lib/api.ts

@@ -32,6 +32,8 @@ export interface ParamDeclaration {
   kind: 'string' | 'number' | 'timestamp' | 'duration' | 'boolean'
   /** A third extraction source, distinct from `capture_group`/`json_field_path`: when true, this param's value is never parsed from text — it's computed as elapsed time since the previous event sharing the same label set. Only meaningful paired with `kind: 'duration'`. */
   elapsed_since_last?: boolean
+  /** Set only for the built-in `ottyl_seq`/`ottyl_ts`/`ottyl_fmt` names, synthesized into `GET /api/params` for discoverability — they're usable in the filter bar (and `ottyl_seq`/`ottyl_ts` in dashboard PromQL queries) without ever being declared, and can't be edited or removed. */
+  reserved?: boolean
 }
 
 export interface TimelineBucket {