fix(research): restore subagent fan-out, record that a skill body and its allowed-tools must agree

research instructed "spawn one subagent per URL" while its allowed-tools
granted no spawn tool, so it silently degraded to serial fetches. Three
other skills spawn subagents without trouble because they declare no
allowed-tools. The defect was the mismatch, not the spawning.

ADR-0027 records the agreement rule. research drops allowed-tools and
gets its steps 4-5 fan-out and the orchestrator-writes gotcha back
(1.0.1 -> 1.1.0).

Closes #116

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EGHFJextYtVQseaHPDDhxB

plugins/bin/.apm/skills/research/SKILL.md

@@ -6,17 +6,8 @@ description: >-
   documentation written from existing code or specs -> `write-docs`. Not a bug
   or incident -> `diagnose`.
 metadata:
-  version: "1.0.1"
+  version: "1.1.0"
   category: research
-allowed-tools:
-  - Grep
-  - Glob
-  - Read
-  - Write
-  - WebSearch
-  - WebFetch
-  - mcp__context7__resolve-library-id
-  - mcp__context7__query-docs
 model: sonnet
 ---
 
@@ -25,6 +16,7 @@ model: sonnet
 - Never infer the output path. A run writes a directory's worth of files, and a guessed destination scatters them through someone's source tree. If the user named no path, stop and ask.
 - Write nothing outside the given output path. A file placed beside the agreed directory is one the user never asked for and will not think to look for.
 - Never write an empty topic file. A stub `troubleshooting.md` reads downstream as researched and closed.
+- Subagents read and summarise; the orchestrator writes every file. A subagent that writes has no view of the other subagents' notes, so its files collide with theirs.
 - A Context7 response that is a "no results" message, a redirect notice, or header-only boilerplate is not coverage. A topic area counts as covered only when the response carries at least one substantive paragraph.
 
 ## Step 1 — Scope against the working directory
@@ -52,11 +44,11 @@ If nothing usable comes back, stop and report what was searched, then ask for st
 
 ## Step 4 — Read the sources
 
-`WebFetch` each URL in turn. No subagent tool is granted here, so the reads are serial and every fetched page lands in this context: reduce each page to notes by topic area, plus the links worth deepening, before fetching the next one.
+Spawn one subagent per URL, in parallel. Each fetches its page with `WebFetch` and returns notes by topic area plus the links worth deepening — never the raw page. The pages stay out of this context; only the notes come back.
 
 ## Step 5 — Deepen
 
-`WebFetch` the links worth following, still one at a time and still reducing each page to notes. Stop a branch once its content turns repetitive or leaves the topic, and cap the whole step at roughly ten additional pages — serial reads make that cap a real budget, not a formality.
+Spawn one further subagent per link worth following, again in parallel and again returning notes only. Stop a branch once its content turns repetitive or leaves the topic, and cap the whole step at roughly ten additional pages.
 
 ## Step 6 — Write