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/CLAUDE.md

@@ -89,6 +89,15 @@ All content commands (post, quick, react, pipeline, first-post, video, multiplat
 
 **Rule:** Always read `assets/voice-samples/` before generating content.
 
+**Invocation form:** Commands invoke plugin agents by their **namespaced** type —
+`subagent_type: linkedin-thought-leadership:<name>` — never the bare `<name>` (a bare
+type does not resolve and the `Task` call fails).
+
+**Reload requirement:** Adding a NEW agent file under `agents/` registers it only after
+a Claude Code **session reload** — the plugin agent set is built at session start, so a
+freshly-added agent (e.g. `fact-checker`, `persona-reviewer` when first added) is not
+invokable until the session reloads. After adding an agent, reload before invoking it.
+
 ## Content Quality Rules
 
 1. Hook: 110-140 characters (mobile cutoff)