feat(pseudo): add code-explanation-as-pseudocode skill

A user-invoked conversational skill: while active, every reply
explains code in commented, human-readable pseudocode instead of
prose. Each answer opens with a source-file-and-approximate-line
anchor, tags notable steps with reference markers ([1], [A]) the
user can point back at, reduces off-topic paths to stubs, omits
low-level mechanics unless asked, defaults to the project main
entry, and never runs longer than one screen.

Dispatches no agents and runs no pipeline; documented in the
README as a conversational skill standing outside the pipeline.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -32,6 +32,14 @@ Two further **utility skills** are invoked on demand rather than as
 pipeline phases: `issue` (file or update a tracker item) and `glossary`
 (build or maintain the project glossary — see `docs/glossary-convention.md`).
 
+One **conversational skill** stands outside the pipeline entirely:
+`pseudo` (typed `/pseudo`) switches replies into commented,
+human-readable pseudocode for explaining code — each answer opens
+with a source-file-and-line anchor, marks notable steps with
+reference markers the user can point back at, reduces the
+irrelevant to stubs, omits low-level mechanics, and never runs
+longer than one screen. It dispatches no agents.
+
 Vocabulary is configurable. A **cycle** is one round in the
 pipeline graph; your project may call it a *release*, an *epic*,
 or whatever fits, and its sub-unit (the default *iteration*) a