Add bulk clear-params action that re-extracts from retained logs (ticket 052)

DELETE /api/params clears the entire standalone-param set — manual and
auto-derived alike — then immediately re-runs auto_declare_params against
every IndexKey::IngestedLog entry still held in the engine's index (oldest
to newest), so params come back fresh from currently-retained log text
without requiring new lines to be ingested. This is a deliberate full
reset, unlike reload_engine_declarations's profile-switch cleanup, which
preserves auto-derived params since those are engine-discovered facts
rather than profile state; here the immediate re-extraction step makes
clearing them safe.

Settings::clear_param_declarations empties the active profile's persisted
params so they don't reappear on restart. The webapp's Params section gets
a single "Clear all" button (with a confirm dialog and a status line
reporting removed/re-derived/logs_considered) rather than a per-param
delete loop; logs_considered surfaces that lines already evicted by
max_logs can't regain their params.

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

webapp/src/lib/api.ts

@@ -287,6 +287,21 @@ export function declareParam(request: ParamDeclaration): Promise<ParamDeclaratio
   return postJson('/api/params', request)
 }
 
+export interface ClearParamsResult {
+  /** How many param declarations (manual + auto-derived) were removed. */
+  removed: number
+  /** How many params were immediately re-derived from log text still retained by the engine. */
+  reextracted: number
+  /** How many retained log lines were re-scanned — lines already evicted by `max_logs` before the clear can't regain their params, so this can be smaller than the total lines ever ingested. */
+  logs_considered: number
+}
+
+// Clears every declared param (ticket 052) and re-derives whatever the engine's still-retained log
+// text supports — see `ClearParamsResult`'s fields for what came back.
+export function clearParams(): Promise<ClearParamsResult> {
+  return sendJson('/api/params', 'DELETE')
+}
+
 export function fetchMetricDeclarations(): Promise<MetricDeclaration[]> {
   return getJson('/api/metrics')
 }