feat: add declarative Director feature actions

docs/DIRECTOR-INTERACTIONS.md

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+# Director scene actions
+
+Version-6 scene documents can attach actions to stable GeoJSON feature IDs in a
+shot's selected data packs. Existing versions 1–5 migrate without adding actions.
+Import validates data and references; it does not load assets or execute actions.
+
+Add `interactions` to a shot, for example:
+
+```json
+{
+  "id": "read-outline",
+  "label": "About this outline",
+  "target": { "packId": "outline", "featureId": "boundary" },
+  "action": {
+    "type": "card",
+    "text": "An authored explanation, displayed as plain text.",
+    "url": "https://example.org/source"
+  }
+}
+```
+
+The target must be a feature in a GeoJSON pack selected by that shot. Points,
+lines and polygons retain stable pack/feature identities. Assets load before
+feature existence is checked; a missing feature refuses the entire action set.
+Images and native media are not interaction targets in this version.
+
+| Action | Fields | Behavior |
+| --- | --- | --- |
+| `card` | `text`, optional `url` | Show plain text and an optional HTTPS source link; never HTML |
+| `focus` | `anchorId` | Set a top-down camera pose at a scene anchor through camera ownership arbitration |
+| `shot` | `shotId` | Load another shot in the same scene at its authored start |
+| `layer` | `layerId`, boolean `enabled` | Request an explicit state through the ordinary layer admission path |
+
+There are at most 64 interactions per shot. Card text is limited to 4,096
+characters; source links cannot contain credentials, query strings or fragments.
+No script, module, arbitrary fetch endpoint or request header is accepted.
+
+Actions appear after LOAD or seek finishes. Click a pack feature to select its
+actions and focus the first button; choose a button explicitly to execute it.
+Tab traverses buttons and Enter/Space activates them. The selected buttons have
+visible outlines, and status feedback is announced to assistive technology.
+There are no global keyboard shortcuts to collide with navigation or typing.
+Drawing ownership blocks both pointer selection and action execution. Camera
+focus uses existing navigation admission, including Cockpit restrictions.
+
+Actions are inactive during automatic playback and camera travel. They do not
+introduce automatic branching or loops. A chain of user-triggered shot changes
+is limited to 64 transitions; an explicit LOAD starts a new chain. Import/Stop,
+replacement, playback and teardown remove selection, cards and picking handlers,
+and abort pending layer requests. No per-frame interaction loop runs.
+
+A layer action must name a layer with an explicit baseline in the current shot.
+A target shot must declare a baseline for every layer the departing shot can
+change. LOAD and seek reapply those baselines and clear selection. Stop cancels
+pending transitions; already completed layer changes remain visible, consistent
+with ordinary scene controls. Camera focus is an immediate anchor pose, not a
+new timeline segment; seek restores the authored camera pose. Scene JSON is not
+modified by executing an action.
+
+The portable interaction session owns action admission/cancellation. The scene
+interaction owner supplies accessible DOM and picking; pack renderers own the
+feature identities and release them with their geometry. Layer/source admission
+and camera arbitration remain with their existing owners.
+
+Visual authoring, import previews and share bundles remain separate follow-up
+work. For now, author actions in scene JSON and use the existing import/export
+controls. Existing content, assets, notices and contributor credit are preserved.