fix: persist workflow step across browser sessions via localStorage

[savinay1986]

Bug

Closing and reopening the browser tab resets the 5-step workflow back to Step 1, losing all visible progress — even though the project data (graph, ontology, etc.) is safely persisted on the backend.

Steps to reproduce:

1. Upload a document and start a simulation project
2. Wait for graph build to complete (Step 1 → Step 2)
3. Close the browser tab
4. Reopen http://localhost:3000/process/<project_id>
5. You land back on Step 1 even though the graph is already built

Root Cause

currentStep in MainView.vue is a plain in-memory Vue ref(1). When loadProject() runs on mount, it correctly restores currentPhase from the backend project status — but never restores currentStep. The two values are independently tracked and only currentPhase was wired to the backend.

Fix

Three targeted changes to MainView.vue:

1. Watcher — watch(currentStep) writes to localStorage under key mirofish_step_{projectId} on every change
2. Restore on load — loadProject() reads back from localStorage after calling updatePhaseByStatus(), restoring the exact step the user left on
3. Status fallback — updatePhaseByStatus() advances currentStep to 2 when status is graph_completed, so even a first-time reload with no localStorage entry correctly skips Step 1

Test Plan

• Upload doc → complete graph build → close browser → reopen URL → lands on Step 2 (Env Setup), not Step 1
• User manually at Step 3/4/5 → close browser → reopen → resumes at correct step
• Brand new project (/process/new) — watcher does not write until real project ID is assigned
• No regressions to existing step navigation or backend polling logic

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