Header polish: drop FLOW label, move chat toggle top-left, drop '· shell' suffix

[mpstaton]

Context:

• Header-Polish-Flow-Label-Chat-Toggle-Placement-Shell-Suffix.md

Three operator findings from the workspace-auth human gate, all in the shell header: the FLOW label duplicates the Flows dropdown; the chat toggle is center-right but its rail is on the LEFT (move toggle top-left, mirroring how queue pairs with its right rail); the wordmark's '· shell' suffix can go.

[mpstaton]

Fourth finding added (doc bumped to 0.0.0.2): an obvious collapse button INSIDE the chat rail header, floated right, sharing visibility state with the shell-header toggle — a rail you open should be closable from the rail itself.