fix(linkedin): close dogfood friction (S14)

Close all 9 friction points from the S13 newsletter dogfood (operator
elected to fix F6-F9 rather than defer):

- F1: namespace all subagent_type calls in newsletter.md to
  linkedin-thought-leadership:<name> (4 sites + canonical note)
- F2: document agent invocation form + reload requirement in CLAUDE.md
  + README.md (reload itself is an operator action)
- F3: add edition-config / edition-delingstekst / edition-HANDOVER
  templates under config/ + wire into Steps 0 and 8 + footer
- F4: reconcile draft path to <serie>/NN-utkast.md (series root)
- F5: de-hardcode series root (explicit arg / LTL_SERIES_ROOT / default)
- F6: config-derive carousel editions (remove Seres CAROUSEL set);
  correct samle comment
- F7: build-html.mjs exits non-zero when zero HTML produced
- F8: guard parseDelingstekst (graceful ENOENT) + correct Step 8 wording
- F9: relocate agents/README.md -> docs/agents-capability-matrix.md

Re-tested: 87/87 plugin tests pass; build-html/build-linkedin behavior
re-verified live. Per-item outcomes logged in dogfood-S13-friction.md.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

plugins/linkedin-thought-leadership/README.md

@@ -217,6 +217,12 @@ trend-spotter --> content-planner --> differentiation-checker --> content-optimi
 
 Parallel support agents: `strategy-advisor`, `analytics-interpreter`, `network-builder`, `content-repurposer`, `video-scripter`.
 
+> **Note (agent invocation + reload):** Commands invoke agents by their **namespaced**
+> type — `subagent_type: linkedin-thought-leadership:<name>`, never the bare name. And a
+> **newly added** agent file under `agents/` only becomes invokable after a Claude Code
+> **session reload** (the plugin agent set is built at session start). Add the agent, then
+> reload before invoking it.
+
 ### Which Agent Do I Need?
 
 | Scenario | Agent |