MeshCore infrastructure page: use mc_is_infrastructure flag (not all observed nodes)

[pskillen]

Problem

/meshcore/infrastructure currently lists all observed MeshCore nodes in the selected time window (GET /api/nodes/observed-nodes/infrastructure/?protocol=meshcore). That is too broad for an “infrastructure” view.

Filtering by something like type=Repeater would be a poor fit: MeshCore roles are looser and less aligned with Meshtastic’s router/repeater semantics than MT meshtastic_role + INFRASTRUCTURE_ROLES.

Proposed approach

Introduce an explicit mc_is_infrastructure boolean on ObservedNode:

• Applies to MeshCore observed nodes only (conceptually separate from Meshtastic infrastructure, which stays role-based).
• Default false; operators mark nodes that should appear on the MC infrastructure page.
• Do not reuse or conflate with Meshtastic role / meshtastic_role infrastructure logic.

API dependency

Blocked by: meshflow-api#367

Item	Notes
Model	ObservedNode.mc_is_infrastructure (BooleanField, default False); only meaningful when protocol=MESHCORE
Migration	Add field + index if needed for list filters
Infrastructure list	GET …/infrastructure/?protocol=meshcore should filter protocol=MESHCORE and mc_is_infrastructure=True (not all MC nodes)
CRUD	Endpoint(s) to set/clear the flag on an observed node (PATCH on observed node detail and/or dedicated action)
Permissions	Only feeders and admins may set or clear mc_is_infrastructure (Django feeder group + is_staff; align with permissions)
OpenAPI	Document field + write operations
Tests	Permission matrix + list filter behaviour

UI work (this repo)

• Consume updated infrastructure API once meshcore filter uses mc_is_infrastructure.
• Operator UI to toggle the flag (node detail and/or MC infrastructure context), gated to feeder/admin.
• Copy on MC infrastructure page explaining explicit marking vs automatic MT roles.
• Update docs/PERMISSIONS.md if new write surface is exposed in UI.

Out of scope

• Changing Meshtastic infrastructure selection (remains meshtastic_role / INFRASTRUCTURE_ROLES).
• Inferring MC infrastructure from repeater/type heuristics alone.

Context

• MC infrastructure page added in PR #306 (branch api-329/pskillen/mc-stats-ui).
• API currently returns all MC observed nodes for protocol=meshcore infrastructure (PR #366).

Acceptance criteria

1. MC infrastructure page shows only nodes with mc_is_infrastructure=true.
2. Feeders and admins can set/clear the flag via API + UI; ordinary users cannot.
3. MT infrastructure behaviour unchanged.