enh(#1243): consume Claude plugin-provided skills in agent_skills (epic #1258 Phase B) (#1261)

* feat(#1243): consume Claude plugin-provided skills via native Skill-tool directive + grant Skill to agent_skills-consumer agents

- Relax global skill name validation to accept namespaced form `^[A-Za-z0-9_-]+(:[A-Za-z0-9_-]+)*$`
- Namespaced names (containing colon) on claude runtime emit a Skill-tool load directive instead of a @-include line
- Namespaced names on non-claude runtimes are skipped with a warning
- Bare unresolved names retain existing warn-and-skip behavior (no promotion to directive)
- Grant `Skill` tool to all 22 agent_skills consumer agents; 5 generated agents updated via research-profiles.cjs + regen, 17 hand-authored agents edited directly
- Add 16 TDD tests in describe('bug #1243') covering happy/mixed/precedence/negative/cross-runtime/regression/grant cases

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* docs(#1243): document plugin-provided skills in agent_skills

Update the Agent Skills Injection reference in CONFIGURATION.md with
the three entry forms (project-relative, global:<name>,
global:<plugin>:<skill>), the Claude-only runtime behaviour of the
namespaced form and the warn-skip on other runtimes, the plugin
pre-install prerequisite, and the consumer-agent Skill tool grant.

Add docs/how-to/attach-a-plugin-skill-to-a-gsd-agent.md with a
step-by-step guide for installing the plugin, locating the namespaced
skill name, wiring it into agent_skills, and verifying injection.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(#1243): align agent_skills docs with emitted block format + mixed-block regression test (code-review)

- Replace two-section mixed-block example (bogus "Load these plugin-provided skills using the Skill tool:" header) with the actual single-section inline format in CONFIGURATION.md and docs/how-to/attach-a-plugin-skill-to-a-gsd-agent.md
- Fix quoted warning text in how-to doc to exactly match the emitted string: [agent-skills] WARNING: Plugin-namespaced skill "global:<name>" requires a Skill-tool-capable runtime (claude) — skipping on runtime "<runtime>"
- Replace phantom agent slugs (gsd-checker, gsd-researcher, gsd-advisor, gsd-synthesizer) in CONFIGURATION.md Supported Agent Types with real agents/gsd-*.md examples (gsd-plan-checker, gsd-phase-researcher, gsd-code-reviewer, gsd-ui-auditor, gsd-research-synthesizer)
- Add byte-identical mixed-block regression test: one path-resolvable global skill + one plugin-namespaced skill on claude runtime → asserts r.ir.block === single-section interleaved block, no secondary header

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* chore(#1243): regenerate agent-size baseline for the Skill-tool grant

The 22 agent_skills-consumer agents each grew +7 bytes from adding `Skill`
to their tools list; refresh the committed per-agent size baseline (#1074 guard).

* chore(#1243): add Added changeset fragment

* fix(#1243): traceable allow-test-rule ref + separator-agnostic byte-identical tests (CI)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/research-profiles.cjs

@@ -24,7 +24,7 @@ const PROFILES = [
       'Researches domain ecosystem before roadmap creation. Produces files in .planning/research/ consumed during roadmap creation. Spawned by /gsd:new-project or /gsd:new-milestone orchestrators.',
     color: 'cyan',
     tools:
-      'Read, Write, Bash, Grep, Glob, WebSearch, WebFetch, mcp__context7__*, mcp__firecrawl__*, mcp__exa__*, mcp__tavily__*, mcp__ref__*, mcp__jina__*',
+      'Read, Write, Bash, Grep, Glob, Skill, WebSearch, WebFetch, mcp__context7__*, mcp__firecrawl__*, mcp__exa__*, mcp__tavily__*, mcp__ref__*, mcp__jina__*',
     requiredIncludes: [
       '@~/.claude/gsd-core/references/research-documentation-lookup.md',
       '@~/.claude/gsd-core/references/research-philosophy.md',
@@ -46,7 +46,7 @@ const PROFILES = [
       'Researches how to implement a phase before planning. Produces RESEARCH.md consumed by gsd-planner. Spawned by /gsd:plan-phase orchestrator.',
     color: 'cyan',
     tools:
-      'Read, Write, Edit, Bash, Grep, Glob, WebSearch, WebFetch, mcp__context7__*, mcp__firecrawl__*, mcp__exa__*, mcp__tavily__*, mcp__ref__*, mcp__jina__*',
+      'Read, Write, Edit, Bash, Grep, Glob, Skill, WebSearch, WebFetch, mcp__context7__*, mcp__firecrawl__*, mcp__exa__*, mcp__tavily__*, mcp__ref__*, mcp__jina__*',
     requiredIncludes: [
       '@~/.claude/gsd-core/references/research-documentation-lookup.md',
       '@~/.claude/gsd-core/references/research-philosophy.md',
@@ -68,7 +68,7 @@ const PROFILES = [
     description:
       'Researches a single gray area decision and returns a structured comparison table with rationale. Spawned by discuss-phase advisor mode.',
     color: 'cyan',
-    tools: 'Read, Bash, Grep, Glob, WebSearch, WebFetch, mcp__context7__*',
+    tools: 'Read, Bash, Grep, Glob, Skill, WebSearch, WebFetch, mcp__context7__*',
     requiredIncludes: [
       '@~/.claude/gsd-core/references/research-documentation-lookup.md',
     ],
@@ -117,7 +117,7 @@ const PROFILES = [
       'Produces UI-SPEC.md design contract for frontend phases. Reads upstream artifacts, detects design system state, asks only unanswered questions. Spawned by /gsd:ui-phase orchestrator.',
     color: 'purple',
     tools:
-      'Read, Write, Edit, Bash, Grep, Glob, WebSearch, WebFetch, mcp__context7__*, mcp__firecrawl__*, mcp__exa__*, mcp__tavily__*, mcp__ref__*, mcp__jina__*',
+      'Read, Write, Edit, Bash, Grep, Glob, Skill, WebSearch, WebFetch, mcp__context7__*, mcp__firecrawl__*, mcp__exa__*, mcp__tavily__*, mcp__ref__*, mcp__jina__*',
     requiredIncludes: [
       '@~/.claude/gsd-core/references/research-documentation-lookup.md',
     ],
@@ -134,7 +134,7 @@ const PROFILES = [
     description:
       'Synthesizes research outputs from parallel researcher agents into SUMMARY.md. Spawned by /gsd:new-project after 4 researcher agents complete.',
     color: 'purple',
-    tools: 'Read, Write, Bash',
+    tools: 'Read, Write, Bash, Skill',
     requiredIncludes: [],
     requiredSeamCalls: [
       'gsd_run query commit',