operator: echo the loop/observation trigger into the panel

[edwin-zvs]

Problem. The operator panel showed the operator's response to each ambient/observation turn (noted, Worked, a finding) but not the input that triggered it — the observation is a Message event, never rendered to the panel's PTY. So watching the panel you saw context-free noted / Worked / noted … and couldn't tell what was being noted.

Two stale-string facts behind this (both from #376):

• The ambient-turn suppression (meant to hide ambient chatter) keyed on "...ambient operator loop tick", but the loop's observation became "...ambient fleet monitor flagged" — so it never fired and responses leaked into the panel.
• The intent has since shifted: responses should be visible (per request), just with their trigger shown.

Change

Before the response streams, the operator echoes the OBSERVATION: trigger into the panel (dim), with the monitor's instruction boilerplate stripped so only the substance shows. The panel now reads question → answer:

│ ambient monitor flagged:
│ s277f8d4 "minibuffer…": blocked waiting at a prompt — "› Write tests for @filename"
noted
* Worked (2s)

Also removes the dead ambient-turn PTY/message suppression — it never fired, contradicts the "show responses" intent, and was a trap (fixing its string would have silently hidden the responses the user wants).

• observation_panel_echo() formats the trigger (strips OBSERVATION: + the monitor boilerplate, dims each line); emitted as PTY before the user Message. Fires for fleet-event observations too, so those replies get context as well.
• Removed ambient_turn detection + both emit_pty=false/emit_messages=false blocks.

The typewriter monolog (#379) is unaffected — it consumes the response Message stream; this echo is PTY-only.

Tests

observation_panel_echo unit-tested (strips marker/boilerplate, keeps substance, None for real user input). 38 interactive tests pass; full build clean. Spec 0024 added.

Visual best confirmed live — after restart, an operator tick shows its trigger then the reply in the panel.