LayerFilter plugin — configurable two-step layer filter

[BhattaraiSijan]

Summary

Adds LayerFilter, a generic, configuration-driven two-step layer filter, built as two cooperating plugins:

• LayerFilterThemes — the far-left theme rail (step 1): pick a high-level theme.
• LayerFilter — the filter panel (step 2): refine within that theme and narrow the layers.

Both are decoupled — they talk only through the app's event bus, with nothing hardcoded into the core.

What's included

Two-step filtering. A far-left rail lists a few high-level themes; selecting one reveals just that theme's filters in the panel beside it. Choosing filters narrows the set of relevant layers, so a mission with dozens of layers collapses to the handful that matter for the task at hand.

Configurable per mission, no code. The themes, each theme's filters, and which layer attribute a filter narrows on are all defined in the mission's configuration and editable in the admin UI — a non-coder can add a theme or filter, and tag layers, without touching code.

Decoupled by design. It's two cooperating plugins that communicate only through the app's event bus — they don't reach into the core or each other. The filter doesn't change layers itself; it announces the matched set so the layer list and other tools can react. The rail's top button signals collapsing the panel the same way.

Matches the design. The rail and panel follow the Figma (theme tokens), with the left panels sitting edge-to-edge.

Scope

Emit-only — it announces the matched layer set on the bus; it does not change layers yet (wiring the layer list to consume that is a follow-up).

Testing

Unit-tested matching and option-derivation (npm run test:unit, Node 20); tsc clean.

Follow-ups

• The layer list reacts to the filter result and updates.
• Friendlier admin-UI editing (raw JSON today) — needs nested form support.
• Populate layer metadata from STAC via an ingest step.

Closes: Issue #163

[github-actions]

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