agents: discussion mode — devs talk in threads; building starts only on explicit signal

Mentioning a dev agent no longer spawns a branch + PR machinery. It is a
CONVERSATION by default: the dev reads what it needs and replies in-thread.

- route.sh: workmode=build|discuss for mode=pr agents. Build ONLY on the
  explicit signals: PR-thread comments (resume), the pm delegation template
  ("please proceed with issue …" — a human can write it too), or the qa bounce
  ("please address my review …"). Everything else = discuss: no branch prep,
  no "🔨 Building" notice.
- run-agent.sh: discussion ACTION for devs (read-only consult, no edits/
  commits/markers). @pm gains 'ASK: @<dev> <question>' to consult devs before
  planning — gather feasibility/effort input, then DELEGATE when enough is
  known. One ASK per reply; never ASK+DELEGATE together.
- publish.sh: pm ASK handler posts the question as a discussion trigger; dev
  discuss path posts the reply (+run report) and skips ALL git/PR machinery
  (stray edits discarded). ASK marker stripped from visible replies.
- agent.yml: WORKMODE threaded to Run-agent + Publish. README documents it.

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

README.md

@@ -36,6 +36,15 @@ deploy-host SSH skill, live in the consuming repo under `.gitea/agent-skills/`
 `@pm` is the only agent that ever merges, and only under the `autopilot` label (its kill switch:
 remove the label mid-flight and the next step reverts to human control).
 
+### Discussion vs building
+
+Mentioning a dev agent is a **conversation by default**: it reads what it needs and replies in the
+thread — no branch, no PR. `@pm` can consult devs the same way with an `ASK: @<dev> <question>`
+marker (gather feasibility/effort input before planning). **Building starts only on the explicit
+signals**: `@pm`'s delegation (*"please proceed with issue …"* — a human can write the same phrase
+to start a build directly), a `@qa` bounce (*"please address my review …"*), or any comment on the
+PR thread itself (resuming existing work).
+
 ### Retros — the learning loop
 
 Ask `@pm` for a retrospective on any issue (e.g. **"@pm run a retro"**, typically when merging). The