Upgrade the Atomic harness to 0.9.26-alpha.6

0.9.26-alpha.6 lets a new session inspect and resume a workflow run
whose owning session crashed (bastani-inc/atomic#3419). On
0.9.26-alpha.5 only the session that started a run could resume it, so
a Planner session opened after a Chopin restart could never recover the
runs the previous server left behind. The five builtin packages are
unchanged, so BUILTINS_OFF still turns off each one for the isolated
Planner.

Assistant-workflow: inline
Assistant-model: Claude Opus 5.5
Assistant-verification: SDK resume repro passed: after kill -9 and the 2-minute live window, a new session's getRun() reported crashed and resume() completed the run on 0.9.26-alpha.6 (rejected with WorkflowRunOwnershipError on 0.9.26-alpha.5)
Assistant-verification: bun test passed: 1912 pass, 2 PostgreSQL skips, 0 fail
Assistant-verification: bun run types passed: all 9 workspace checks
Assistant-verification: bun run ci passed: dprint, oxlint, tokens, design contract, design record, Impeccable (no new findings)
Assistant-verification: source check passed: @bastani/atomic 0.9.26-alpha.6 dist/builtin lists intercom, mcp, subagents, web-access, workflows
Co-authored-by: Alex Lavaee <lavaman131@github.com>