feat(lessons): a lesson is readable, writable and browsable by a human (#3734)

Step 7's actual UI. Before this the frontend had zero lesson code — the kind
existed for agents only, which is rule 27 failing.

THE EDITOR ASKS FOR THE TRIGGER BY NAME, and leads with it. Three fields —
the trigger, the claim, the detail — never one markdown box. That is the
design step 1 settled, and the evidence is blunt: the snippet corpus carries
a trigger on every record with no guard anywhere, because a service composes
the title from a named parameter. What is at 100% is a named structured
field, not a writer remembering a convention. The trigger gets the most room,
its own explanation, and a save button that refuses without it and says why.

The form shows the composed title live, so the writer is agreeing to a
document they can read rather than one assembled out of sight. A 409 from the
duplicate gate is rendered as the record that already covers the moment, with
a link to improve it and an explicit override — not as a failure.

THE BROWSE VOCABULARY GAINS THE KIND, which #3161 warned this step not to get
wrong: a facet chip, a badge label, and routing to `/lessons/:id` rather than
the note editor, which cannot edit a trigger. The badge is neutral alongside
snippet and process — a hue would make the softest record in the corpus look
like the loudest, next to a rule that actually binds.

BOTH DIRECTIONS OF THE PROVENANCE. The detail page resolves `learned_from` to
titles rather than bare ids, because "#4181" tells a reader nothing about
whether it is worth opening. And `LessonsTaughtPanel` answers the reverse on
the record's own page — the direction the task body calls the one that gets
forgotten. It has no author to type it, which is exactly why it tends never
to get built. A component, not markup in the task editor, so the same panel
mounts on any record a lesson can cite instead of being written a second time
(#3207). Silent when empty: most records taught no lesson, and a panel that
says "None yet" everywhere is one people learn to skip.

GLOBAL-BY-DEFAULT IS MADE LEGIBLE. A lesson meeting you on a project it was
not written on reads as a bug unless the page says otherwise, so the origin
line says it as a property of the kind rather than as an apology.

Design system tokens throughout; no new raw hex. `--fs-error` rather than
`--fs-danger` — 31 uses against 1.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

frontend/src/views/TaskEditorView.vue

@@ -23,6 +23,7 @@ import WordCount from "@/components/WordCount.vue";
 import TagInput from "@/components/TagInput.vue";
 import ProjectSelector from "@/components/ProjectSelector.vue";
 import MilestoneSelector from "@/components/MilestoneSelector.vue";
+import LessonsTaughtPanel from "@/components/LessonsTaughtPanel.vue";
 import TaskLogSection from "@/components/TaskLogSection.vue";
 import DiffView from "@/components/DiffView.vue";
 import ConfirmDialog from "@/components/ConfirmDialog.vue";
@@ -546,6 +547,13 @@ useEditorGuards(dirty, save);
         <!-- Work log -->
         <TaskLogSection v-if="taskId" :task-id="taskId" class="body-log" />
 
+        <!-- What came OUT of this record. The forward link is typed by
+             the lesson's author; this direction has no author and so
+             tends never to get built — but a reader opening an old
+             issue wants to know what was learned from it. Silent when
+             there is nothing, because most records taught no lesson. -->
+        <LessonsTaughtPanel v-if="taskId" :record-id="taskId" />
+
         <!-- Applicable rules (plan tasks only) -->
         <PlanRulesPanel
           v-if="store.currentTask?.task_kind === 'plan' && store.currentTask?.project_id"