tui(operator): placeholders for untyped names, underlined text inputs

[edwin-zvs]

Two affordances for the operator and channel editors, as requested:

1. Placeholders instead of prefilled defaults on create. The operator editor's Name and the channel editor's Channel ID start empty and show their suggested value as a dimmed placeholder. Typing starts from a blank field instead of appending to a value the user never wrote. A save that leaves the field untyped adopts the suggestion, so the one-keystroke create flow still works. The pane title borrows the placeholder while the name is empty, and the new-operator picker action now opens the draft editor directly — the separate "Operator name:" prompt is retired, with its duplicate-name check moved to save time (a create colliding with an existing operator is refused with a note instead of silently overwriting it).
2. Underlined input areas on free-text fields. While a free-text field is selected, its value renders underlined and padded to a minimum input width — the rows that accept typing are now visibly inputs next to the rows that cycle (kind, trigger, routing…) or toggle (state, disclosure). Applies to both editors across all kinds (http / slack / slack-personal), driven by shared field-classification helpers so the render and the key handling cannot drift apart.

Before / after

	before	after
naming an operator
new channel ID

Full clips (same input stream driving both binaries): before.mp4 · after.mp4 — media is committed at d77b769 and removed in the follow-up commit; the pinned links stay alive via the PR ref.

Testing

• Updated the create-flow tests to the new direct-open shape; new tests: draft opens with empty name + placeholder and the title borrows it; typing renames the draft keystroke-by-keystroke; save adopts an untyped name/ID; duplicate create names refused at save; next-free suggestion (operator → operator-2); channel editor renders the dimmed ID placeholder with an underlined input area (buffer-modifier assertion).
• Full workspace suite green; recorded flows above exercised against a live isolated daemon.

🤖 Generated with Claude Code