feat(#1866): agent-side self-load of configured agent_skills

Each of the 22 consumer agents now self-loads its configured agent_skills
in its mandatory init step, so .planning/config.json agent_skills.<type>
reaches the agent on every runtime — including Cursor and /gsd-autonomous,
where Skill()-delegated workflow bash init did not reliably execute.

- gsd-core/references/agent-skills-bootstrap.md: shared contract
  (query + Read + dedup guard that skips when <agent_skills> is already
  in the prompt, so Claude's orchestrator-side injection never doubles)
- 22 agents/gsd-*.md: one self-load line naming the agent's own type
- gsd-core/workflows/autonomous.md: note that delegated agents self-load
- tests/agent-skills-bootstrap.test.cjs: regression + parity (CONSUMER_AGENTS
  bijection + fast-check property) — Generative-Fix-Divergence guard
- docs: ADR-1866, CONFIGURATION dual-injection How It Works, INVENTORY
  row, Changed changeset

Closes #1866

tests/agent-size-baseline.json

@@ -1,36 +1,36 @@
 {
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-  "gsd-code-reviewer.md": 16780,
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   "gsd-debug-session-manager.md": 14159,
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   "gsd-doc-synthesizer.md": 9782,
   "gsd-doc-verifier.md": 12403,
-  "gsd-doc-writer.md": 38834,
+  "gsd-doc-writer.md": 38924,
   "gsd-domain-researcher.md": 6998,
-  "gsd-eval-auditor.md": 12362,
+  "gsd-eval-auditor.md": 12452,
   "gsd-eval-planner.md": 7008,
-  "gsd-executor.md": 43343,
+  "gsd-executor.md": 43433,
   "gsd-framework-selector.md": 6778,
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+  "gsd-integration-checker.md": 15238,
   "gsd-intel-updater.md": 18122,
   "gsd-mempalace-curator.md": 4160,
-  "gsd-nyquist-auditor.md": 7255,
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   "gsd-pattern-mapper.md": 12487,
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   "gsd-user-profiler.md": 8516,
-  "gsd-verifier.md": 49124
+  "gsd-verifier.md": 49117
 }