refactor(dashboard): decommission the Graph view (Vue Flow node canvas) (#1689)

[dolho]

What

Removes the dashboard's Graph mode (the legacy Vue Flow node canvas). Grid (magnetic tile canvas) and Timeline (default) cover fleet overview; Graph was a parallel render path (drag/positions, fit-view, reset-layout) plus four @vue-flow/* deps that no longer earned their upkeep.

Acceptance criteria — all met

• Mode toggle offers only Grid / Timeline; all viewMode === 'graph' branches removed from Dashboard.vue (graph canvas, graph-only Reset Layout button, on-load fitView).
• 'graph' removed from VIEW_MODES in network.js; node-position persistence removed (nodePositions, save/load/reset, onNodeDragStop + exports). setViewMode's invalid-mode fallback flipped 'graph' → 'timeline'. Shared state (working state, circuit-breaker map, the nodes computed Timeline consumes) preserved.
• A persisted 'graph' preference degrades gracefully to the default — the VIEW_MODES.includes() guard at init and in setViewMode both route it to timeline (no error, no blank canvas).
• AgentNode.vue + SystemAgentNode.vue deleted (Graph was their only consumer — verified). Also deleted TagClouds.vue (the graph-canvas viewport tag-cloud layer, likewise orphaned).
• All four @vue-flow/* removed from package.json; package-lock.json regenerated so npm ci stays consistent. No @vue-flow import remains anywhere.
• e2e updated (dashboard-grid-view.spec.js): the graph-mode assertions are gone; the smoke test now covers Grid↔Timeline coexistence.
• Docs updated: architecture.md (dropped the Vue Flow tech-stack entry; dashboard modes now Grid/Timeline; rewrote the stale "Collaboration Dashboard" entry, which named a non-existent AgentCollaboration.vue) + the dashboard-grid-view feature flow.

Notes

• ReplayTimeline stays (Timeline-mode replay, explicitly out of scope). It builds its lane tiles from the shared nodes computed's node.data (display_label, is_system, autonomy, avatar) — so the nodes machinery is kept; only the graph-only position/draggable persistence is removed (positions default, unrendered).
• The Collaboration data (X-Source-Agent detection, agent_collaboration WS events) still flows and feeds Timeline — only the Vue Flow node-graph rendering is gone.

Verification

All touched SFCs compile via @vue/compiler-sfc; network.js passes node --check; grep confirms 0 @vue-flow imports (package.json + lockfile both clean). Verified against the live stack: dashboard returns 200, the Vite-served network.js shows VIEW_MODES = ['grid', 'timeline'], and the Vite-transformed Dashboard.vue has 0 graph imports.

(Frontend build/e2e run in CI — node_modules here is root-owned from the Docker build, so npm ci + the Playwright suite are the mechanical gate.)

Related to #1689

🤖 Generated with Claude Code

Fixes #1689

[vybe]

Validated via /validate-pr: grepped the head branch for every dangling reference — zero hits for AgentNode/SystemAgentNode/TagClouds, the removed store functions (saveNodePositions/loadNodePositions/resetNodePositions/onNodeDragStop), any @vue-flow/* import, and any remaining 'graph' literal. Stale localStorage['trinity-dashboard-view'] = 'graph' degrades to timeline via the VIEW_MODES.includes() guard, and the invalid-mode fallback in setViewMode moved off 'graph'. e2e green. All ACs met.

Minor (non-blocking, follow-up): getNodeColor() in Dashboard.vue is now dead — its only consumer was the Vue Flow MiniMap.