Feature request: live simulation from user position (GPS/browser geolocation)

[heigre]

Feature request

Add a User Position mode that uses device/browser geolocation (with explicit permission) to continuously update a live simulation from the user's current location.

Problem

Users in the field (especially on phones) need quick, real-time signal insight from where they currently stand, without manually creating/moving Sites repeatedly.

Goal

When location is available, LinkSim should provide a live, continuously updating simulation centered on the user's current position, including map visualization and a reachable-sites list.

Proposed behavior

• Browser prompts the user for location permission before any geolocation use
• If granted, app tracks location updates (watch mode) and refreshes simulation when position changes
• Render live simulation overlays from current user position
• Show table/list of PASS-reachable Sites from current position (aligned with issue Feature request: show PASS-reachable sites table when a site is selected #413)
• Provide clear UI states for: waiting for permission, tracking active, permission denied, unavailable/unsupported, and stale location
• Allow user to stop/pause tracking at any time

Platform notes

• Should work across desktop/mobile browsers where geolocation is supported
• Must gracefully handle platform differences and permission model variations

Scope

• New user-position driven workflow (UI + client logic)
• No automatic persistent data writes unless user explicitly saves

Acceptance criteria

• User is explicitly asked for location access by the browser
• Live simulation updates as user location changes
• PASS-reachable sites list updates alongside map simulation
• Clear fallback/empty/error states exist for denied or unsupported geolocation
• Feature can be turned off by the user

Related issues

• Feature request: show PASS-reachable sites table when a site is selected #413 (PASS-reachable sites list/table)
• Add user location flow with map centering and temporary site creation #250 (user location flow and map centering)

[heigre]

Clarification: this is Phase 2 (advanced) of the user-position workflow.\n\nThis issue extends #250 by adding continuous geolocation tracking and continuously updated simulation outputs (including PASS list integration with #413).\n\nImplementation order suggestion: complete #250 foundation first, then layer this mode on top.