feat(sub-accounts): rename sub-account inline

[vipineth]

Parent PRD

#75

What to build

Add a rename action to each sub-account row in the management view. A pencil icon next to the name activates inline editing: the name cell switches to a text input pre-filled with the current name. Saving (Enter or a confirm button) calls exchange.subAccountModify({ subAccountUser, name }). On success the cell returns to read mode showing the new name. On failure an error is shown inline and the previous name is restored.

Acceptance criteria

• Pencil icon is visible next to each sub-account name in the management view
• Clicking the pencil switches the name cell to an editable text input pre-filled with the current name
• Input enforces the 1–16 character constraint with live feedback
• Pressing Enter or clicking a confirm control submits the rename
• Pressing Escape cancels and restores the original name
• On success: cell returns to read mode showing the new name (no full list refetch required, but acceptable)
• On error: input remains open, error message displayed

Blocked by

• Blocked by feat(sub-accounts): sub-account management view with Trade action #77 (management view must exist)

User stories addressed

• User story 4 (rename a sub-account inline)
• User story 21 (feedback when rename completes)
• User story 23 (list reflects updated name)

[vipineth]

Closing as wontfix. Sub-account switching was reverted in 990bff4 — the store, hook, and user-menu wiring no longer exist. This issue's spec assumes those modules. If sub-accounts return, we'll file fresh issues against the current codebase.