Extend Properties Panel to feature + sub-feature editing in plot view

[IanMayo]

Problem

#447 delivers Properties-Panel editing at plot + catalog-browser level, but analysts also need to tag/annotate metadata inside an open plot at finer granularity:

• Feature level — per-track fields like debrief:feature_tags, display name, nationality, vessel class/type/role overrides (these are already first-class in the schema after Add specification for event-sourcing undo with tunable provenance #181).
• Sub-feature level — per-track-point metadata (e.g., labels, classification, analyst notes on a single fix within a track).

Today none of these are editable from the UI. Feature-level fields are populated by import + save-time registry resolution (#183). Sub-feature metadata has no schema slot at all — track-point properties currently carry only time/kinematic data.

Proposed Solution

Extend the Properties Panel shell introduced in #447 so its 4th ActivityPanel section swaps contents based on selection.primary / selection.featureIds:

1. Feature editor — when exactly one feature is selected, edit its schema-defined editable fields (debrief:feature_tags, per-platform overrides on TrackProperties). Stages in session-state, flushes on save (consistent with plot-level behaviour).
2. Sub-feature editor — when a track-point path is primary (e.g., track-1/42), edit point-level metadata. Requires a LinkML schema extension first to define which fields a track point carries (e.g., label, tags, note).

Selection flow already supported: features slice tracks selection.featureIds + selection.primary; nested-child selection (#53) encodes point index as track-id/index.

Provenance entry per save (Article III), same pattern as #447.

Success Criteria

• Selecting one feature shows an editable form for that feature's schema-defined fields; edits stage in Zustand and persist on plot save.
• Selecting a track point shows a form driven by the new point-metadata schema; edits stage and persist.
• Selecting multiple features shows a read-only summary (no bulk edit in v1).
• Form is generated from schema — adding a new feature or point field in LinkML auto-appears.
• Clearing selection falls back to the plot-level editor from Add Properties Panel for editing STAC plot & catalog metadata #447.
• Provenance log entry for every saved edit.
• Works fully offline.

Constraints

• Depends on Add Properties Panel for editing STAC plot & catalog metadata #447 (panel shell, schema-driven form renderer, provenance wiring).
• Sub-feature editing requires a LinkML schema change — ship that as an internal step within this item (not a separate backlog row) since it's tightly coupled.
• Must not regress catalog-browser editing delivered in Add Properties Panel for editing STAC plot & catalog metadata #447.
• Reuse the existing features slice in session-state; no new selection store.
• Use the same ParameterEditor-style widget set as Add Properties Panel for editing STAC plot & catalog metadata #447.

Out of Scope

• Bulk edits across multiple selected features.
• Editing geometry / coordinates (this is metadata only).
• Sub-feature editing for non-track features (annotation shapes, etc.) — revisit after track-point pattern proves out.
• Reverting an override to its auto-derived value (covered by a separate follow-up if needed).

Related

• Add Properties Panel for editing STAC plot & catalog metadata #447 — Properties Panel shell (prerequisite)
• feat: Add STAC catalog overview panel with map and timeline #135 — auto-populate STAC extension props on save
• Add specification for event-sourcing undo with tunable provenance #181 — per-platform override fields on TrackProperties (shipped)
• Configure VS Code extension activity visibility #53 — nested-child selection (provides point-path format)