Style concept callouts as brand-lavender info boxes

Both in-page callouts in docs/concepts/observability.md (the new
proposal-0054 bundling note and the pre-existing Langfuse SDK
version compatibility note) were using `!!! note`, which renders in
Material's default blue. The 13 example walk-through pages use
`!!! info "Source"`, which the project CSS paints in the brand
lavender. Flip the two concept-page callouts to `!!! info` so every
admonition site-wide picks up the same brand styling.

Also refresh the now-stale CSS comment that claimed the only
`!!! info` usage was the Source box.

Author: chris-colinsky

docs/concepts/observability.md

@@ -581,7 +581,7 @@ async def persist(state: PipelineState) -> Mapping[str, Any]:
 `graph.drain()` but scoped to one invocation. Returns the same
 `DrainSummary` shape, with the same timeout discipline.
 
-!!! note "drain_events_for ships in v0.12.0 alongside the read API"
+!!! info "drain_events_for ships in v0.12.0 alongside the read API"
     `CompiledGraph.drain_events_for` is the spec §6 / proposal 0054
     pair to the §9.4 accumulator lifecycle described above. The two
     proposals are bundled into the v0.12.0 release cycle as
@@ -933,7 +933,7 @@ same in tests and production. See
 [`examples/langfuse-observability`](../examples/langfuse-observability.md)
 for a runnable demo.
 
-!!! note "Langfuse SDK version compatibility"
+!!! info "Langfuse SDK version compatibility"
 
     Validated against `langfuse>=4.6,<5`. The v4 SDK introduced an
     OTel-based architecture with `start_observation` /

docs/stylesheets/extra.css

@@ -285,18 +285,19 @@
   padding-left: 0.75rem;
 }
 
-/* Source-box callout color (the ``!!! info "Source"`` admonition
- * inserted between the H1 and lead paragraph on every example
- * walk-through doc). Material's default ``info`` admonition uses
- * a blue accent; this override paints it in the project lavender
- * to match the ``#9d4edd`` brand purple and inline-code color
- * (``#e4c1f9`` ≈ rgb(228, 193, 249)) used elsewhere in the slate
- * theme. Scoped to ``.admonition.info``; currently the only
- * ``!!! info`` usage in the docs is the Source callout, so this
- * effectively styles "the Source box". If a future doc adds a
- * non-Source info admonition that should stay blue, switch the
- * walk-through callouts to a custom ``!!! source`` type and
- * re-scope this rule to ``.admonition.source``. */
+/* Brand-lavender callout color, applied to every ``!!! info``
+ * admonition site-wide. Material's default ``info`` admonition
+ * uses a blue accent; this override paints it in the project
+ * lavender to match the ``#9d4edd`` brand purple and inline-code
+ * color (``#e4c1f9`` ≈ rgb(228, 193, 249)) used elsewhere in the
+ * slate theme. Two usage shapes in the docs today:
+ *   - the ``!!! info "Source"`` box inserted between the H1 and
+ *     lead paragraph on every example walk-through page; and
+ *   - in-page concept callouts (e.g. the proposal-0054 bundling
+ *     note in ``concepts/observability.md``).
+ * If a future doc needs a generic info admonition that stays in
+ * Material's default blue, switch this rule to a custom
+ * ``!!! brand`` admonition type and migrate the existing call sites. */
 .md-typeset .admonition.info,
 .md-typeset details.info {
   border-color: rgb(228, 193, 249);