refactor(session): finish sessionless runtime cutover

[LichKing-2234]

Summary

• switch git-hook checkpoint flow to a true sessionless workspace-based path
• stop wiring retired legacy session bootstrap services into backend runtime and drop dead internal services
• align dashboard/runtime docs and frontend copy with tracked workflows and the sessionless model

Test Plan

• cd ae-cli && go test ./... -count=1
• cd backend && AE_TEST_POSTGRES_DSN='postgres://postgres:postgres@127.0.0.1:15432/postgres?sslmode=disable' go test ./internal/toolusage ./internal/checkpoint ./internal/handler ./cmd/server -count=1
• cd frontend && pnpm test

[Copilot]

Pull request overview

Completes the cutover to the sessionless attribution runtime: the backend stops wiring/serving legacy session bootstrap and session-event/usage services, the git-hook queue and post-commit/post-rewrite paths derive a workspace_id (instead of requiring a session marker) and emit unbound checkpoints, and the dashboard/repo-detail copy is realigned to "Tracked Workflows" and ae-cli attribution sync. Docs (architecture, staged-cutover spec, plan) are updated to reflect the landed state.

Changes:

• Delete sessionbootstrap, sessionusage, sessionevent services/tests, the SessionUsageHandler, and the session bootstrap wiring + stale-session sweeper in cmd/server/main.go; update router signature and all handler tests accordingly.
• Replace dashboard active_sessions with tracked_workflows (distinct workspace_id over tool_usage_events) end-to-end (Go handler, Vue dashboard/types, unit/e2e tests).
• Rework ae-cli/internal/hooks queue + handler to be workspace-keyed (NewWorkspaceQueue, PendingWorkspaceIDs, workspace-derived binding_source, workspace collector cache) while keeping a legacy session queue path.

Reviewed changes

Copilot reviewed 34 out of 34 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
frontend/src/views/repos/RepoDetailView.vue	Update unbound-repo copy to reference ae-cli attribution sync.
frontend/src/views/DashboardView.vue	Show tracked_workflows metric instead of active_sessions.
frontend/src/types/index.ts	Rename DashboardData.active_sessions to tracked_workflows.
frontend/src/tests/repo-detail-view.test.ts	Assert new attribution-sync copy.
frontend/src/tests/dashboard-view.test.ts	Use tracked_workflows in mocked dashboard payload.
frontend/e2e_test.py	Update Playwright assertion to "Tracked Workflows".
docs/superpowers/specs/2026-05-14-legacy-session-staged-cutover-design.md	Rewrite to describe landed cutover and remaining footprint.
docs/superpowers/plans/2026-05-14-legacy-session-staged-cutover.md	Mark plan completed and refresh remaining gaps.
docs/architecture.md	Drop proxy/session bootstrap from diagrams and component table.
backend/internal/sessionusage/{service,service_test}.go	Delete legacy session-usage service.
backend/internal/sessionevent/{service,service_test}.go	Delete legacy session-event service.
backend/internal/sessionbootstrap/{service,service_test,key_selection,key_selection_test}.go	Delete legacy session bootstrap package.
backend/internal/handler/session_usage.go	Remove session-usage handler.
backend/internal/handler/router.go	Drop sessionBootstrapSvc parameter and import.
backend/internal/handler/efficiency.go	Compute tracked_workflows from distinct tool_usage_events.workspace_id.
backend/internal/handler/handler_*_test.go	Update SetupRouter arg counts and dashboard test data to tool-usage events / tracked_workflows.
backend/cmd/server/main.go	Remove session bootstrap construction, stale-session sweeper, and unused constants/import.
ae-cli/internal/hooks/queue.go	Add NewWorkspaceQueue/PendingWorkspaceIDs; reroute legacy queue under attributionlocal root.
ae-cli/internal/hooks/queue_test.go	Re-key queue tests to workspace IDs.
ae-cli/internal/hooks/handler.go	Derive workspace_id, emit unbound checkpoints when no marker, flush by workspace, persist workspace collector cache.
ae-cli/internal/hooks/handler_test.go	Switch tests to workspace markers, add unbound checkpoint test, update cache path assertions.
ae-cli/internal/collector/collector.go	Add WriteWorkspaceCache.
ae-cli/cmd/{test_helpers_test,hook_test}.go	Configure origin remote and derive workspace_id in cmd hook tests.

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[LichKing-2234]

I did not change this in the current PR. The metric rename here is intentional and the value is currently defined as accumulated distinct workflow identities, not a recency-window activity gauge. Changing it to a time-windowed count-distinct would alter the product metric semantics and should be handled as a separate follow-up rather than folded into this runtime-cutover slice.