docs(specs): add Offline-Support spec and plan for discussion

[jl-0]

Adds specs/Offline-Support/{spec.md,plan.md} drafting a phased PWA / offline mobile field workflow:
Phase 1 — PWA shell (installable, app-shell SW, status pill)
Phase 2 — User-driven AOI tile pre-cache
Phase 3 — Durable Draw mutation queue with server-wins conflict tray
Phase 4 — GPS path capture tool (LineString save via sync queue)

Each phase is independently shippable behind a server-side feature flag. Documents are intended as a discussion starting point and call out open questions on auth, attachments, cross-origin layers, and release strategy.

Using this PR as a method to do some discussions on the plan and see what we think

[github-actions]

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[fcalef]

Some thoughts on the Phases:

Phase 1 — PWA shell (installable, app-shell SW, status pill)
Sounds good. Curious how much this is a separate branch or just a modification of our mobile interface or something else?

Phase 2 — User-driven AOI tile pre-cache
Agreed, pre-cache a local tileset is important for full offline or even weak cell service areas.

Phase 3 — Durable Draw mutation queue with server-wins conflict tray
Not sure what this means, but I think it's to address conflicts with many users providing input?

Phase 4 — GPS path capture tool (LineString save via sync queue)
This is an important one that will need to be able to tap into a phone/tablet GPS signal.

Suggested additional task:
Phase 5 - image capture and logging from local device. Allow a user to take single or multiple images of a location, record the devices position OR have images automatically assigned to a pre-recorded feature (i.e. point, line, polygon), and store that image(s) in a way that's accessible by MMGIS.

Phase 6 - data synching with 'home' server once within network range. Network detection? Webhook enabled data syncing? Manual vs automated? Must include vector file and image transfer.

Phase 7 - audio/video capability similar to image capture? i.e. assignable to a vector feature?