FetchTimeseries: feature clicks to chart-series events

[BhattaraiSijan]

Summary

Adds FetchTimeseries, a no-UI plugin bridging feature:click to the chart-series contract: on a vector feature click it reads the layer's variables.timeseries block over the bus (layers:getConfig), templates the fetch URL from the clicked feature ({properties.<key>}, {id}, {lon}, {lat} — unresolvable placeholders surface as named errors, not silent no-ops), fetches with abort-on-supersede, normalizes the response, and emits plugin:fetch-timeseries:* events for SeriesChart.

Normalization handles both response shapes the VEDA features API serves under content negotiation — GeoJSON FeatureCollections and flat rows — via loose properties.-prefix path resolution, plus groupBy (one series per parameter), unitKey, and auto-detected time/value keys.

Layers opt in per mission config; clicks on layers without the block do nothing. enabled: false disables without deleting. Charts persist until the next click replaces them (single chartId). The README documents the config schema and a working EPA AQS demo.

Merge order

1. Emit feature:click on the bus for every vector feature click #292 feature:click core event — merge before this PR (runtime dependency; no compile dependency)
2. SeriesChart: chart-series contract and single-variable chart plugin #293 SeriesChart (this PR's git base)
3. this PR

Testing

tests/unit/fetchTimeseries.spec.js (31 cases): config gating incl. enabled:false, URL templating and its error cases, response mapping for both API shapes, grouping/units, payload building. Full unit suite green.

Manual: add the README's timeseries block to the AQS layer in Configure, click a station — loading → chart with the parameter picker. Station 54-39-20 ("Dixie St.") exercises 15 parameters across 5 units.